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 production2 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]. 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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.