Overview of Water Shutoff Operations in Oil and Gas Wells

chemengineering

Article Overview of Water Shutoﬀ Operations in Oil and Gas Wells; Chemical and Mechanical Solutions

Abdullah Taha and Mahmood Amani * Department of Petroleum Engineering, Texas A&M University at Qatar, P.O. Box 23874, Doha, Qatar; [email protected] * Correspondence: [email protected]

Received: 23 January 2019; Accepted: 10 May 2019; Published: 14 May 2019

Abstract: This paper provides an integrated overview of the water shutoff operations, starting from the causes to the solutions. The paper begins with explaining the benefits of eliminating excessive water production. Then, the different types of water production and their properties are explained. The paper also focuses in reviewing the disadvantages of producing unwanted water as well as the sources of it, followed by an explanation of the methodology for identifying the problem. Then, the chemical solutions for water shutoff are reviewed which are generally applied to solve the excessive unwanted water production in the reservoir or near the wellbore area. Finally, the paper illustrates the common mechanical solutions for water shutoff within the wellbore. The aim behind this paper is to provide a general description of identifying the unwanted water production sources and the common practices for water shutoff operations.

Keywords: unwanted water; fractures; aquifer; logging; polymer ﬂooding; plugs

1. Introduction Excessive water production is one of the main well-known problems that would face any oil operator in the world. Although this problem is typical in older wells, it can also occur in new developed wells as well [1]. It causes numerous economic problems for oil production companies. First, excessive water effects the performance of the production wells and shortens their lifespan. The presence of the water in the wellbore increase the weight of the fluid column which leads to an increase in the lifting requirements [2]. That increases the operating cost and leads to a lower the drawdown. For example, if the well is a gas lifted well, the amount of gas injected to lift the fluid from the wellbore to the surface is higher with the production of excessive water than without producing it. Water production also enhances the presence of scales, corrosion, and degradation in the field facilities starting from the wellbore to the surface facilities [2]. Another major problem is that the cost of separating, treating, and disposing the produced water is a great burden to oil company budgets. It costs around $1 billion/year in Alberta to dispose of the produced water [3]. Getting rid of that kind of production helps in reducing expenses for the operators and increases the profitably of their operations [4]. Therefore, water shutoff operations are essential. Finally, with good knowledge of the formation characterizations and the unique challenges of the field, unnecessary water production can be avoided from the wellbore designing phase [5].

2. Types of Water Production Is water production always a bad thing? The right answer is deﬁnitely: no! Water is one of the most important drives for oil production since it helps in managing the reservoir, mobilizing the oil, and displacing it in the homogenous rocks. This water is known as necessary or good water production. It is the water that is typically associated with oil production in the late stages of water-ﬂooding

ChemEngineering 2019, 3, 51; doi:10.3390/chemengineering3020051 www.mdpi.com/journal/chemengineering ChemEngineering 2019, 3, 51 2 of 11 operations or from active aquifers. It is also the water produced at a low water/oil ratio (WOR) which maintains the profitably of a production well [1]. Attempts to reduce this kind of water production leadsChemEngineering directly to reduction2018, 2, x FOR inPEER the REVIEW oil production [6]. On the contrary, unwanted water production 2 of 11 is the type which needs to be eliminated and reduced in order to increase the productivity and the flooding operations or from active aquifers. It is also the water produced at a low water/oil ratio profitability of the production wells [7]. Water shutoff operations focus on eliminating unwanted water (WOR) which maintains the profitably of a production well [1]. Attempts to reduce this kind of water production,production which leads is alsodirectly called to reduction ‘bad water’. in the This oil kind production of production [6]. On createsthe contrary, problems unwanted other water than those mentionedproduction previously, is the type such which as needs reduced to be oil eliminated production and reduced and poor in sweeporder to eincreasefficiency the within productivity the matrix rocks.and Put the simply, profitability that means of the losing production money! wells The [7]. worst Water problem shutoff amongoperations unwanted focus on water eliminating production issuesunwanted is the unswept water production, areas and oilwhich pockets is also that called are left‘bad behind water’. asThis a result kind of badproduction conformance creates jobs. This caseproblems is commonly other than known those mentioned in water-flooding previously, operations such as wherereduced water oil prod is simplyuction and injected poor throughsweep the injectionefficiency well towithin displace the matrix oil toward rocks. thePut productionsimply, that means well and losing to maintainmoney! The the worst pressure problem of the among reservoir however,unwanted the water water goesproduction to an openissues fracture is the unswept or high area permeabilitys and oil pockets layer. that It are is all left about behind the as resistancea result of of bad conformance jobs. This case is commonly known in water-flooding operations where water is the paths in the reservoirs. The least resistance path is the winner in attracting the injected water toward simply injected through the injection well to displace oil toward the production well and to maintain it and the oil in the matrix rock stays behind without achieving the required sweep to attain efficient the pressure of the reservoir however, the water goes to an open fracture or high permeability layer. oil sweepingIt is all about or good the resistance conformance of the [paths3]. If in the the production reservoirs. The well least happens resistance to be path connected is the winner to the in open fractureattracting or the the high injected permeability water toward layer, it unwantedand the oil in water the matrix production rock stays would behind occur. without It is essentialachieving to be able tothe di requiredfferentiate sweep between to attain those effi twocient types oil sweeping of water or production good conforma in ordernce [3]. to If maintain the production the productivity well of thehappens well. One to be of connected the ways to identifythe open thefracture type ofor thethe excessivehigh permeability water production layer, unwanted in a certain water well is byproduction studying thewould off setoccur. wells’ It is wateressential cut to behavior. be able to Itdifferentiate is bad water between production those two ifthe types off ofset water wells are producingproduction with in a muchorder to lower maintain water the cut productivity [4]. of the well. One of the ways to identify the type of the excessive water production in a certain well is by studying the offset wells’ water cut behavior. It 3. Sourcesis bad water of Unwanted production Water if the Productionoffset wells are producing with a much lower water cut [4].

After3. Sources discussing of Unwanted the problems Water Production associated with unwanted water production, it is important to identify the reasons which lead to this kind of production in order to be able to accomplish a successful After discussing the problems associated with unwanted water production, it is important to wateridentify shutoff theoperation. reasons which In water-flooding lead to this operations,kind of production the aim in is order to mobilize to be able the oilto inaccomplish the matrix a rock towardsuccessful the production water shutoff wells operation. and to maintainIn water-flooding the pressure operations, of the the reservoir. aim is to mobilize Open fractures the oil in and the high permeabilitymatrix rock layers toward usually the production reduce the wells efficiency and to main of floodingtain the operationspressure of the and reservoir. leads to Open poor fractures conformance. As mentionedand high permeability previously, layers the fluid usually tends reduce to take the the efficiency paths leastof flooding resistance operations and the and injected leads to water, poor as a result,conformance. goes to the openAs mentioned fractures previo and highusly, permeability the fluid tends formations to take the instead paths of least matrix resistance rock to and displace the the oil. Ininjected some cases,water, theas a water result, injection goes to the well open happens fractures to beand connected high permeability with the formations production instead well through of an openmatrix fracture rock to or displace features the which oil. In are some known cases, also the aswater ‘thief injection zones’ well [8] (Figurehappens1). to Open be connected features with also can the production well through an open fracture or features which are known also as ‘thief zones’ [8] result in an excessive amount of water if they are connected to the aquifer (Figure2). Additionally, (Figure 1). Open features also can result in an excessive amount of water if they are connected to the fractures and open features can contribute to unwanted water production when they are connected aquifer (Figure 2). Additionally, fractures and open features can contribute to unwanted water to waterproduction formations when/ zonesthey are [9 ].connected Gas hydrate to water reservoirs formations/zones can be also [9]. aGas main hydrate source reservoirs of excessive can be water productionalso a main when source dissociated of excessive [10]. water production when dissociated [10].

FigureFigure 1. Example 1. Example of of a watera water injection injection wellwell connected to to an an oil oil producer producer well well through through an open an open featurefeature/high/high permebility permebility layer. layer. ChemEngineering 2019, 3, 51 3 of 11 ChemEngineeringChemEngineering 20182018,, 22,, xx FORFOR PEERPEER REVIEWREVIEW 3 3 of of 11 11

FigureFigureFigure 2. 2.2.An AnAn oil oiloil producer producerproducer connected connectedconnected to to an an aquiferaquifer throughthrough through anan an openopen open feature.feature. feature.

AnotherAnotherAnother common commoncommon source sourcesource of ofof unwanted unwantedunwanted water waterwater productionproducproductiontion isis is waterwater water coning.coning. coning. ThisThis This situationsituation situation usuallyusually usually occursoccursoccurs when whenwhen the thethe production productionproduction zone zonezone is isis near nearnear thethethe aquiferaquiaquiferfer or or water water formationsformations formations withwith with aa adecentdecent decent permeablepermeable permeable connectionsconnectionsconnections between betweenbetween the thethe oil production oiloil productionproduction zone zonezone and the andand water thethe formation.waterwater formation.formation. Coning ConingConing arises with arisesarises the with drawdownwith thethe ofdrawdowndrawdown the pressure ofof whichthethe pressurepressure encourages whichwhich theencouragesencourages water to thethe migrate wawaterter toto migratemigrate the wellbore toto thethe fromwellborewellbore the from bottomfrom thethe(Figure bottombottom3 ). Although(Figure(Figure it3).3). can AlthoughAlthough be controlled itit cancan bebe by controlledcontrolled decreasing byby the decreadecrea ratessingsing of production, thethe ratesrates ofof it production,production, is not a favorable itit isis notnot approach aa favorablefavorable since oilapproachapproach production sincesince is goingoiloil productionproduction to be reduced isis goingoing asg toto well bebe reducedreduced [8]. It can asas wellwell be also [8].[8]. solvedItIt cancan bebe by alsoalso plugging solvedsolved byby the pluggingplugging bottom ofthethe the well,bottombottom however, ofof thethe it well,well, is considered however,however, itit as isis a conscons shortideredidered term asas solution aa shortshort [termterm6]. solutionsolution [6].[6].

FigureFigureFigure 3.3. WaterWater coning. coning. ChemEngineering 20192018,, 32,, 51x FOR PEER REVIEW 44 of 11 11 ChemEngineering 2018, 2, x FOR PEER REVIEW 4 of 11 One of the most common sources of unwanted water production is poor conditions of the nearby One of the most common sources of unwanted water production is poor conditions of the nearby wellbore.One ofThis the kind most of common production sources typically of unwanted can occur water as productiona result of casing is poor leaks conditions or bad of cement the nearby jobs wellbore. This kind of production typically can occur as a result of casing leaks or bad cement jobs wellbore.behind the This casings kind which of production usually creates typically channels can occur connecting as a result the of unwanted casing leaks water or badproduction cement behind the casings which usually creates channels connecting the unwanted water production jobsformations/sources behind the casings with which the wellbore. usually The creates casing channels and the connecting cement job the behind unwanted the casing water are production supposed formations/sources with the wellbore. The casing and the cement job behind the casing are supposed formationsto create a /sealsources from with such the unwanted wellbore. layers The casing(Figures and 4 and the cement5). job behind the casing are supposed to create a seal from such unwanted layers (Figures4 4 and and5 ).5).

Figure 4. Poor cement behind the casing with a channel connecting water source to the wellbore. Figure 4. PoorPoor cement cement behind behind the the casing casing with with a a cha channelnnel connecting water source to the wellbore.

Figure 5. Casing leak connecting the wellbore with water formation. Figure 5. Casing leak connecting the wellbore with water formation. 4. Identifying the Problem 4. Identifying the Problem 4. IdentifyingReducing the excessive Problem water production usually starts with gathering all available reservoir and Reducing excessive water production usually starts with gathering all available reservoir and productionReducing data. excessive Then logging water production tools are used usually to locate starts the with water gathering entry points. all available Finally, reservoir based on and the production data. Then logging tools are used to locate the water entry points. Finally, based on the productionresults, a proper data. shuto Thenff loggingmethod tool is useds are [11 used]. The to mostlocate important the water part entry in anypoints. water Finally, shuto ffbasedoperation on the is results, a proper shutoff method is used [11]. The most important part in any water shutoff operation results,the accurate a proper diagnosis shutoff of method the problem. is used It is[11]. essential The most to know important the water part entry in any point, water the shutoff heterogeneity operation of is the accurate diagnosis of the problem. It is essential to know the water entry point, the isthe the reservoir accurate rocks, diagnosis dominant of production the problem. mechanisms, It is essential and the to schematics know the of thewater wellbore entry [12point,]. In fact,the heterogeneity of the reservoir rocks, dominant production mechanisms, and the schematics of the heterogeneityall available information of the reservoir about rocks, the well dominant is considered production valuable, mechanisms, like drilling and operations the schematics reports, of logs, the wellbore [12]. In fact, all available information about the well is considered valuable, like drilling wellboreand production [12]. In history. fact, all The available reason behindinformation that is ab thatout every the well well is would considered have its valuable, own workflow like drilling based operations reports, logs, and production history. The reason behind that is that every well would operationson it is properties, reports, history, logs, and and production reservoir heterogeneity. history. The reason Accurate behind investigation that is that leads every to success well would in the have its own workflow based on it is properties, history, and reservoir heterogeneity. Accurate havewater its shuto ownff operation, workflow increasing based on oil it production,is properties and, history, saving waterand reservoir handling costs.heterogeneity. Fayzullin Accurate et al. [13] investigation leads to success in the water shutoff operation, increasing oil production, and saving investigationpresent an example leads to of success a case in study the water for understanding shutoff operation, unwanted increasing water oil production production, in and an Eastern saving water handling costs. Fayzullin et.al. [13] present an example of a case study for understanding water handling costs. Fayzullin et.al. [13] present an example of a case study for understanding ChemEngineering 2019, 3, 51 5 of 11

Europe gas field. Production logging tools in production wells usually are used to identify the water production zones, which is an important step in planning for an optimized water shutoff operation. For water injection wells, water flow logs are used to identify the thief zones. However, horizontal wells are challenging in identifying the problem as well as in the intervention part. That is due to the complicity of the wellbore, flow regimes, and their effects on obtaining the required information. Luckily, advanced production logging tools can be used to identify the entry points as well as the rates [2]. Fiber optics technologies are used nowadays along with logging tools to ensure high quality real time data that help in accurately identifying the water entry zones [14]. Al-Zain et. al. [15] present a case of successful usage of fiber optics to shut off unwanted water production in an oil field. In addition to that, water/oil ratio (WOR) plots can be used to identify the excessive water production problems. In fact, it can be a more effective tool than logging in many cases as explained in [16]. For channeling behind the casings, running cement bond logs or ultrasonic pulse-echo logs plays a vital role in ensuring the integrity of the cement job behind the casing. Those kinds of logs evaluate the bonding properties of the cement job behind the casing and point out bad cement areas. For casing leaks, production, temperature, and noise logs are all means of identifying the sources of leaking [8].

5. Chemical Solutions Far from the wellbore, in the reservoir or near the wellbore, water shutoff operations can be performed by several chemical treatments. Those chemical solutions lead to better conformance in the reservoir as well as blocking the unwanted water production zones. The idea is to be able to close the paths of least resistance in front of the water by reducing their permeability in order to prevent the water from coming to the wellbore through them. Also, they aid in forcing the water to mobilize and displace the oil in the reservoir. In other words, the aim is to block the open features and high permeability channels to force water to go toward the harder path to sweep oil from the matrix rock that results in higher overall economical returns than producing oil from fractures. In fact, induced formation damage can be used as an effective solution to control the unwanted water production [17]. The results of chemical solutions can be achieved in a couple of months to years, depending on the nature of the reservoir and the properties of the injected chemicals. The main advantage that chemical water shutoff operations have over mechanical operations is that they solve the problem of the unwanted water production instead of hiding it under or behind a plug, packer, or tubing patch. Injected chemicals can reach water features in the reservoir and reduce the permeability, resulting in closing them entirely. They also have the freedom of moving between the layers and features which helps in reaching to far extents and completely closing them. Another use of chemical injection is to increase the viscosity of the injected fluid which leads to a better sweeping efficiency and eventually reduces the production of unwanted water. The success of chemical injection operations depends on the knowledge level of the reservoir and its characterizations, chemical properties, and accurate placement of the injected chemicals [3,18]. For example, the effectiveness of water shutoff agents depends highly on the properties of the reservoir and has to be compatible with the reservoir temperature and water salinity in order to achieve an effective water shutoff [19]. In this section, common chemical solutions are discussed in detail, along with examples of the execution of the operations.

5.1. Gel Gel injection is one of the most famous chemical solutions for water shutoff operations. It is used to reduce the water oil ratio and increase the conformance of the pattern. That happens through the ability of the gel to reduce the permeability and block the open features, fractures, and high permeability water zones. It can be applied in the wellbore, near the wellbore, and far from the production well through injection wells. It is very effective in reducing the permeability of unwanted zones and has proven its ability to improve the sweep efficiency and shutting-off the unwater water zones. The injected gel is mainly made of water, small volumes of polymers and crosslinking chemical agents [6]. Gel treatments can completely seal off layers; therefore, they are considered aggressive ChemEngineering 2019, 3, 51 6 of 11 and risky conformance control operation [3]. On the other hand, polymer gel injection is considered relatively cheaper than other improved oil recovery operations. Gel injection operations are divided into three main stages: modeling, designing, and executing. The first step is to model the gel injection operation by using simulation software, which is an important step for designing the program of gel injection operation [18]. In this stage, all the available information about the reservoir and the well are considered valuable, such as: reservoir parameters, water entry points, drilling operations reports, logs, and production history. The second step is to design the properties of the polymer gel fluid. Injecting gel in the reservoir depends on four properties. First one is the viscosity of the gel at the time of injection which helps in directing the gel to the lager and least resistance paths. Second is the nature of the gel phase which is usually chosen to be the aqueous phase since the water is the desired phase to be shut off. Third is the density of the gel. It very important to be designed carefully and based on the density of the formation water to avoid losing the effectiveness of the gel treatment. Fourth is the setup time or injection time. Longer injection time leads to more success in allowing the gel to seal off larger features and least resistance paths [3]. Al-Dhafeeri et. al. [20] present a case study of using gel treatments as a chemical solution to seal the excessive water zones.

5.2. Polymer Flooding Another common technique for water shutoff operations is the usage of the polymer flooding method to increase the viscosity of the water. This technique is applied to increase the viscosity of the drive fluid (water) which helps in mobilizing and displacing the oil in the reservoir matrix rock. This technique is usually applied in the reservoir far from the production wells through water injection wells to achieve better sweeping efficiency in the reservoir. That eventually leads to preventing excessive water production. The usage of polymer flooding is very common among the oil operators and it can be prepared by dissolving the polymers in the injected water and inject it through injection wells. Polymers used in this technique are usually two types: biopolymers and synthetic polymers. Biopolymers’ advantages over the synthetics are that they are not affected by the salinity of the water and they are insensitive to the mechanical degradations. However, they are more expensive than synthetic polymers. Xanthan and scleroglucan are two famous kinds of biopolymers. Synthetic polymers are more common since they are cheaper, more available, and perform well with low-salinity water. Polyacrylamide (PAM) and hydrolyzed polyacrylamide (HPAM) are two types of synthetic polymers. Polymers can also play a role in reducing the permeability if the molecular weight is increased [6]. Finally, based on the characteristics of the reservoir and the economics of the operations, the right polymer is chosen in case of chemical injection [21]. El-Karsani’s paper [22] includes an overall review of the polymer systems used for water shutoff operations along with their chemical compounds and properties. There are other chemical techniques for water shutoff operation such as resins, solid particles, and foams which are also effective in obtaining better conformance and enhance the sweep efficiency. More details about those methods can be found in [6]. Finally, Bybee [23] presented a case of a long horizontal well with excessive water production from southern Italy. Sealant was pumped as a solution to successfully solve the problem.

6. Mechanical Solutions Within the wellbore, there are available technologies which can successfully shut off the unwanted water production. The impact can be seen in hours in contrast to the chemical solutions which was discussed in the previous section. Controlling the water production mechanically is known for it is fast outcomes as well as its cheap costs. It is usually a rigless job, which means a lower cost [2]. Mechanical water shutoff operations are preferred by operators since they are relatively cheaper than chemical solutions [4]. Once more, an accurate diagnosis is essential before attempting to apply those solutions, since it can result in losing the oil production from the well. That can be achieved, as mentioned previously, through running logs to identify the water production zones. In the case of ChemEngineering 2019, 3, 51 7 of 11 mechanical shutoff operations, there are some factors affecting the success of them. One of them is the setting depth of the plug or the packer can be wrong due to inaccurate readings from the coiled-tubing meter. The reservoir conditions also play a great role in affecting the operations, since a cross flow between the layers can happen and leads intervention to failure. The wellbore condition is another vital factor which needs to be considered. Scale presences in the tubing can result in failure of the operations, since it can create an obstacle while running the plug or the packer downhole. Wells with high deviation angles can be challenging to run in hole with coiled-tubing since they can get stuck a lot [24]. In this section, common mechanical solutions are discussed in details along with examples of the execution of the operation.

6.1. Plugs and Packers One of the most well-known mechanical solutions for water shutoff and isolation operations inside the wellbore is the installation of packers and plugs. They are successful in eliminating the production from unwanted water zones. They are commonly used by oil operators to aid the wells performance and shut off the excessive water production [25]. This hardware is known for being economical and reliable in achieving isolation since it can be installed without pulling the production tubing and without the drilling rig. They can be installed by using coiled tubing which can run them through the wellbore. Also, the results can be achieved relatively fast, in a couple of hours to days, in contrast with chemical injection solutions. Simply, the concept of packers and plugs is a small diameter element, mainly rubber, which can expand downhole the wellbore into larger diameters, creating a seal and isolating the well from unwanted features or zones [26]. There are different types of packers and plugs with different properties and setting techniques. Some elements expand by interacting with certain types of fluids (oil, water, or hybrid) which are known as ‘swellable packers’. They also depend on pre-designed properties like temperature, pressure, and salinity of the formation fluid. That can be a disadvantage in some cases and leads to failure in setting the element. If those properties are not accounted for accurately, that might lead to a faster inflation of the elements or even slower inflation than expected. In the worst case scenario, the element might not inflate at all. Other packers and plugs inflate by applying pressure on the element in order to expand and seal. These types of plugs usually inflate by pumping darts, steel balls, or fluid to apply pressure on the rubber element and allow it to expand and increase its diameter. Packers and plugs can be used to isolate unwanted water production inside the wellbore in certain cases. An easy example would be an open-hole well completion and the water zone is identified to be from the bottom of the well. A bridge plug can be installed to isolate the bottom section and shut down the additional water production to aid the production performance from upper oil zones (Figure6). The di fficulty increases if the water source happens to be in the middle or at the top part of the production section of the tubing in the reservoir section. In that case, a blank pipe with upper and lower packers, with a pre-designed length, can be installed to isolate the water production area without compromising the lower and upper oil production zones (Figure7). In the case of a multi-lateral wells, if one of the laterals is watered-out or producing extreme amounts of unnecessary water, it can be abandoned by setting a plug to isolate it from other laterals. The usage of packers is also used in early stages of the well life, specifically in the completion stages after drilling. That is a common practice for operators who have a reasonably decent knowledge of the expected features and layers of their reservoir. Also logging while drilling tools can be an asset by identifying the open features which might be the future reason for bad water production. After drilling the well and collecting the data, a pre-perforated liners can be installed with packers to produce only the good layers and isolate the risky formations. Once more, an accurate and cautious pre-design of the job is essential for designing the elements to avoid failures. ChemEngineering 20192018,, 32,, 51x FOR PEER REVIEW 88 of 11 11 ChemEngineering 2018, 2, x FOR PEER REVIEW 8 of 11

Figure 6. Using a plug to shut off oﬀ the productionproduction of water from thethe bottom.bottom. Figure 6. Using a plug to shut off the production of water from the bottom.

Figure 7. Two packers above and below a blank pipe to shut ooffff thethe productionproduction ofof waterwater fromfrom thethe Figure 7. Two packers above and below a blank pipe to shut off the production of water from the middle and upper intervals without compromisingcompromising otherother oiloil productionproduction zones.zones. middle and upper intervals without compromising other oil production zones. Likewise, forfor water water injection injection wells, wells, those those plugs plug cans be can used be to used insure to better insure conformance better conformance outcomes Likewise, for water injection wells, those plugs can be used to insure better conformance andoutcomes to eliminate and to theeliminate production the production of bad water of frombad water the production from the wellsproduction through wells thief through zones, highthief outcomes and to eliminate the production of bad water from the production wells through thief permeabilityzones, high permeability layers, or connected layers, openor connected features. Foropen example, features. if anyFor ofexample, the previous if any features of the have previous been zones, high permeability layers, or connected open features. For example, if any of the previous identifiedfeatures have in the been injection identified profile in ofthe water injection injection profile well, of water plugs caninjection be used well, to isolateplugs can injected be used water to features have been identified in the injection profile of water injection well, plugs can be used to fromisolate going injected into them.water Iffrom there going is an into open them. feature If atthere the bottomis an open of a waterfeature injection at the bottom well, a plugof a canwater be isolate injected water from going into them. If there is an open feature at the bottom of a water installedinjection towell, isolate a plug the can bottom be installed section, to to isolate avoid the wasting bottom the section, injected to water avoid and wasting direct the it intoinjected oil matrix water injection well, a plug can be installed to isolate the bottom section, to avoid wasting the injected water rocksand direct instead. it into Similarly, oil matrix if the rocks feature instead. happens Similarl toy, be if at the the feature middle happens or the top to be of theat the injection middle profile, or the and direct it into oil matrix rocks instead. Similarly, if the feature happens to be at the middle or the atop blank of the pipe injection with upper profile, and a blank lower pipe packers withcan uppe ber installedand lower to packers isolate thecan thiefbe installed zones from to isolate stealing the top of the injection profile, a blank pipe with upper and lower packers can be installed to isolate the thethief injected zones waterfrom withoutstealing compromisingthe injected water the conformance without compromising and the sweeping the conformance efficiency of theand field the thief zones from stealing the injected water without compromising the conformance and the (Figuresweeping8). efficiency of the field (Figure 8). sweeping efficiency of the field (Figure 8). ChemEngineering 2019, 3, 51 9 of 11 ChemEngineering 2018, 2, x FOR PEER REVIEW 9 of 11

Figure 8. TwoTwo packers above and below a blank pipe to av avoidoid injecting the water in open features or high permeability layers.

Other thanthan that,that, inflatable inflatable packers packers are alsoare usedalso inused chemical in chemical injection injection for water for shuto waterff operations. shutoff operations.As mentioned As previously,mentioned previously, chemicals can chemicals be used can in the be nearused wellborein the near area wellbore to control area and to control shut off andthe shutunwanted off the water unwanted production. water However,production. this However, operation this considered operation risky considered because risky of the because high cost of andthe highthe risk cost of and injecting the risk the of chemicalsinjecting the into chemicals the oil production into the oil zones production [27]. Therefore, zones [27]. packers Therefore, are packers used to aredirect used the to flow direct of thethe injectedflow of chemicalsthe injected into chemic the desiredals into layers the desired and prevent layers fluid and fromprevent going fluid into from the goingproduction into the formation. production Packers formation. create aPackers seal by create inflating a seal and by isolating inflating the and upper isolating and bottom the upper intervals and bottomto make intervals sure that to chemicals make sure do that not chemicals bypass to oildo zones.not bypass to oil zones.

6.2. Tubing Tubing Patches This method is mainly used for fixing fixing well integrity issues particularly casing leaks. The casing leaksleaks problems problems are are common in in old wells and the wells which are completed in formations with corrosive gasesgases likelike HH22S[S [28,29].28,29]. IfIf thethe sourcesource of of the the unwanted unwanted water water was was found found to beto be from from a leak a leak in the in thecasing, casing, squeezing squeezing cement cement or resins or resins patches patches is considered is considered to be to a be suitable a suitable solution. solution. This This method method can canbe applied be applied only only after after identifying identifying the exact the exact location location of the of leak the through leak through the methods the methods discussed discussed earlier. earlier.Squeezing Squeezing jobs can jobs be performedcan be perf byormed rigs by or sometimesrigs or some withtimes current with current technologies technologies can be acan rig-less be a rig- job. lessUsually, job. Usually, inflatables inflatables are used are to direct used theto direct patches the toward patches the toward leaking the point leaking [30]. point For small [30]. leaks,For small fine leaks,cement fine particles cement are particles squeezed are tosqueezed fix the well to fix integrity the well issue integrity as well issue as creatingas well as a sealcreating [28]. a seal [28].

7. Conclusion 7. Conclusion Excessive water production causes numerous economic problems for oil production companies Excessive water production causes numerous economic problems for oil production companies such as effecting the performance of the production wells, shortening their life period, increasing the such as effecting the performance of the production wells, shortening their life period, increasing the operating cost, enhancing the presence of scales, corrosion, and degradation in the field facilities. It is operating cost, enhancing the presence of scales, corrosion, and degradation in the field facilities. It very important to distinguish necessary water from unwanted water production since any attempt to is very important to distinguish necessary water from unwanted water production since any attempt reduce good water leads directly to reduction in the oil production. Unwanted water production can be to reduce good water leads directly to reduction in the oil production. Unwanted water production identified by comparing the problematic well with offset producer water cut values. Unwanted water can be identified by comparing the problematic well with offset producer water cut values. Unwanted production can occur through connected open fractures or high permeability zone, water coning, water production can occur through connected open fractures or high permeability zone, water coning, casing leaks, and poor cement behind the casing. It is essential to identify the water entry point through production logging tools and study all the available information about the well in order ChemEngineering 2019, 3, 51 10 of 11 casing leaks, and poor cement behind the casing. It is essential to identify the water entry point through production logging tools and study all the available information about the well in order to execute a successful water shutoff operation. Based on the case, chemical or mechanical solutions can be applied to shut off the unwanted water production. Chemical solutions are considered as permeant solutions and are more risky. Mechanical solutions are easier in execution and faster in achieving results. This paper provided a summary for the water shutoff operations starting from explaining the problem, the way to identify it, and finally the available common chemical and mechanical solutions to overcome the unwanted water production problem.

Author Contributions: A.T. conducted most of the Literature Review and case studies, and M.A. provided, guidance, supervision, assisted with the writing and editing of the paper. Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂict of interest.

References

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