WELL COMPLETIONS Problems Related to Squeeze Cementing S. H. SHRYOCK HALLIBURTON CO. MEMBER A/ME LOS ANGELES, CALIF. K. A. SLAGLE DUNCAN, OKLA. Abstract Terminology Downloaded from http://onepetro.org/JPT/article-pdf/20/08/801/2221721/spe-1993-pa.pdf by guest on 27 September 2021 Causes of problems relating to squeeze cementing oper­ Breakdown ations are presented. Much has been written on materials' The language used in squeeze cementing is rather loose and techniques"" that have been used in particular areas, and .subsequently leaves much to the imagination of those but little mention is made of some problems that occur expected to execute the job. During training sessions held during the operation. by one of the major oil companies the past 2 years, drill­ ing people were presented with the question, "What is Introduction your definition of a breakdown?" Recognizing that a ma­ jority of those present were from California oil fields, and Squeeze cementing generally can be described as the that the major application for squeeze cementing is that process of forcing a cement slurry into holes in the casing of supplementing a faulty primary job to obtain 1solation and cavities behind the casing. These operations are usu­ of an oil zone from adjacent water zones as required by ally performed during drilling and completion of a well, the California Division of Oil and Gas, the type of squeeze or for repairing or altering a well at some later date. job that was foremost in their minds was that of squeezing Squeeze cementing is necessary for many rellisons, but prob­ water-shut-off holes. There were two definitions expressed ably the most important use is to segregate hydrocarbon most frequently: producing zones from those formations producing other fluids. The key factor on a squeeze cementing job is that (1) That pressure necessary to break down or fracture of placing the cement at the desired point or points neces­ the formation so that it will accept fluid. sary to accomplish the purpose. (2) That which must be done before one can attempt Squeeze cementing problems are closely related to man's a squeeze cementing job. ability to understand the earth's properties once its crust Breakdown actually is a poor name for what really needs has been penetrated. It is often difficult to determine why to be attained on most squeeze jobs since the prominent some wells can be squeezed successfully with one job while problem is in the well bore, and the desired performance others in the same field require four or five jobs. There is for the perforations and cavities to accept fluid without seem to be a number of opinions as to the proper method fracturing. Fractures normally will accept the cement of squeeze cementing. We are not attempting to argue or slurry and often great volumes of it, but not necessarily in find fault with these opinions; rather we hope to approach the area that needs repair. Obtaining a fracture on the alnd recognize problems that do occur in such a manner breakdown will more often than not cause extra rig time, that we might learn to consider ways in which to solve require greater volumes of cement, and create lost time them. waiting on cement-all of which are costly. Applications of Squeeze Cementing Fracture Gradient A term closely related to breakdown and one that needs Some of the most pertinent applications for squeeze to be understood is formation fracture gradient, which is cementing that need consideration are: (1) supplementing a the pressure! foot of depth required to create a fracture. primary cementing job that may be deficient because of Also of interest is the fact that propagation and extension channeling or insufficient fillup (Fig. 1); (2) reduction or of a fracture usually require a lower pressure than was elimination of water intrusion from above or below the needed for its creation. Too often it is assumed that over­ hydrocarbon producing zone (Fig. 3); (3) reduction of the burden lifting is necessary for a fmcture to occur. Also, GOR by isol3!ting the oil zone from an adjacent gas zone; due to average formation density, the fracturing gradient (4) repair of a casing leak that might have deVeloped due to is anticipated to be at least 1 psi! ft of depth. This is a corrosion, pressure parting or joint leaks (Fig. 2); and (5) good round number and easy to use in calculations, but abandoning of old perforations or plugging of a depleted or experience has indicated that due to structural stresses in watered-out producing zone. the earth and elasticity of the earth's formations, fractures usually occur at less than 1 psi! ft and often as low as 0.6 psi! ft. Original manuscript received in Society of Petroleum Engineers office Oct. 9. 1967. Revised manuscript received June 20. 1968. Paper (SPE 1993) was presented at SPE 38th Annual California Regional Meeting Downhole Treating Pressure held in Los Angeles. Calif.• Oct. 26-27. 1967. © Copyright 1968 Ameri­ can Institute of Mining. Metallurgical, and Petroleum Engineers, Inc. After it is recognized that the formation may fracture 'References given at end of paper. at a pressure lower than may be generally anticipated, the AUGUST, 1968 801 problem becomes one of defining a maximum pressure that pressure was applied in an attempt to obtain 7,400 psi on can be used safely. Since the fracture gradient is pertinent the pumps at the surface. At a pressure of 4,350 psi, the to the subsurface formation in question, and the allowable perforations broke down and again started taking fluid pressure to avoid fracturing equals the gradient times the quite readily. The entire 100 sacks of cement was displaced depth, we are concerned with the downhole treating pres­ without obtaining any indication of another buildup. 1ihree sure. This is a combination of hydrostatic pressure and additional squeeze cement jobs using 475 sacks of cement surface pump pressure less whatever may be lost as fric­ were needed before a job was successful. tion due to velocity during pumping. Because this latter What happened? Pressure of 4,350 psi at the surface factor probably will be relatively small during a squeeze added to a hydrostatic pressure of 3,700 psi exerted by job-approaching zero as the pumping rate is decreased-it 7,400 ft of 72 lb/ cu ft mud created a pressure of 8,050 psi might be advisable to consider frictional pressure loss as a at the perforations, in contrast with 5,800 psi downhole portion of the safety factor, minimizing fracture potential. On breakdown pressure. The explanation for this relatively this basis the maximum surface pump pressure would be high pressure is loss of filtrate from the high fluid loss the allowable downhole treating pressure (fracture gradient slurry during the hesitation period and deposition of im­ times depth) minus the hydrostatic head of cement slurry mobile cement filter cakes in the perforations. However, and other fluids in the tubing, and less whatever ,safety since a WSO test normally is made in a shale section, only factor is considered desirable. In some areas the safety a limited quantity of filter cake was formed because there factor used is 300 psi. was no place for large volumes of filtrate to go. The squeeze We might consider a case to illustrate more clearly this pressure increased enough to move the filter cake; pres­ terminology confusion. An oil company manual on meth­ sure was applied directly on the formation at a gradient Downloaded from http://onepetro.org/JPT/article-pdf/20/08/801/2221721/spe-1993-pa.pdf by guest on 27 September 2021 ods of cementing oil wells stated that a pressure gradient of about 1.09 psi/ft; and a fracture was created and ex­ of 1.0 psi/ ft should be used in calculating pressures for a tended away from the wellbore with the remainder of the squeeze job. Personnel responsible for directing and super­ slurry. In all probability the application of pressure suffi­ vising the job calculated what WClJS thought to be an accept­ ciently weakened the formation around the wellbore so able squeeze pressure in accordance with the manual and that two additional squeezes were required to re-stabilize proceeded with the job to squeeze off water-shut-off the area before the operation was satisfactory. (WSO) holes that had tested wet. The depth at which the What might have been done to reach this excessively squeeze job was to be performed was 7,400 ft, and the hole high pressure that was mistakenly calculated? Allowing contained drilling mud with a density of 72 Ib/ cu ft (hy­ time for the cement either to set or dehydrate more ex­ drostatic gradient of 0.5 psi/ft), which also was to be used tensively probably would have produced a very high final as the displacement fluid. A breakdown was obtained squeeze pressure. However, only limi,ted value would result when the surface pressure reached 2,100 psi (downhole because all this pressure would have been contained with­ treating pressure of 5,800 psi) with the perforations ac­ in the casing and would not apply to the annular area. cepting fluid at a rate of 25 cu ft! min. One hundred sacks This squeeze job was probably a success when only 20 of neat cement (hydrostatic gradient of 0.82 psi/ ft) were sacks were displaced and pressure began to rise, but it mixed, injected into the tubing and displaced to just below degenerated rapidly into an expensive failure. the packer. Initially it was difficult to obtain any pressure buildup, and not until 20 sacks had been displaced did any Job Design indication of a buildup occur.