Field Test Results With Alkaline Potassium Solutions To Stabilize Clays Permanently
- Ben F. Sloat (Tiorco Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- May 1990
- Document Type
- Journal Paper
- 143 - 146
- 1990. Society of Petroleum Engineers
- 5.6.5 Tracers, 5.4.1 Waterflooding, 1.2.3 Rock properties, 5.2 Reservoir Fluid Dynamics, 2.2.2 Perforating, 1.1.1 Wellsite Preparation, 2.4.3 Sand/Solids Control, 2.7.1 Completion Fluids, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 3 Production and Well Operations, 4.1.2 Separation and Treating, 6.5.4 Naturally Occurring Radioactive Materials, 6.5.2 Water use, produced water discharge and disposal
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The use of concentrated KOH to stabilize clays is becoming a common practice in Wyoming. Seventy-two injection wells, ranging from single pilots to fieldwide programs, have been treated and monitored since the technology was first introduced in Aug. 1984. This paper summarizes test results that fall into three broad categories: (1) those that increase recoverable reserves, (2) those that speed the rate of waterflood oil recovery, and (3) those that do more harm than good. Wells in the first two groups are examined starting with treatment design and wellsite preparation and moving on through the pumping stages to final evaluation of the results. The mixing and handling of highly alkaline solutions are covered from the service company and operator safety viewpoints, and with respect to the fluid-quality, chemical, and metallurgical requirements for proper placement of the solutions. Two wells are singled out for their special contribution to the Teaming-curve aspect of this new technology and for their value in helping to avoid making the same mistakes again.
The ability of concentrated KOH to stabilize clays permanently was established in 1981. From this start, controlled field tests began in 1984. The first step toward general use of the process was Sloat and Larsen's paper covering very closely monitored injection-wed treatments. (A thorough reference list on the subject is provided in Ref. 2.) This paper summarizes, by formation, 46 of the 72 treatments performed during the past 3 years. The Upper Cretaceous Shannon sand (Table 1) has shown the best results, with average post-treatment rates of 193 B/D [30.7 m3/d] per vertical porosity foot. The experience obtained from these treatments has allowed process designs to advance to where KOH application is normal practice in some zones. In all cases, the fluids (both oil and water) that would be contacted by the process were analyzed before treatment. Most crude oils were screened for interfacial tension (IFT) reduction and reactivity with KOH. Table 2 includes eight screenings taken from a total data base of more than 300 crude oils, The most recent program (Line 39, Table 3) made use of new diversion technology to improve the distribution of the presoak and to allow the KOH to contact more of the low-permeability rock.
The clay-stabilization process consists of three basic steps: a preflush, the actual KOH injection, and a postflush. The purpose of the preflush is to move as much of the divalent-ion content as possible away from the near-wellbore area. The KCl concentration in the preflush should be greater than the total dissolved solids content of the formation water. In all cases, the solution should be filtered to at least 10-um quality. The preflush can serve a dual purpose by being pumped at different rates and pressures to develop data points useful for step-rate test work. The preflush also can contain thiocyanate or nitrate tracer to confirm the well as a source of water breakthrough or as an aid in defining directional permeability. The preflush should be pumped at a rate that exceeds the rate at which the oil rises up the tubing. Again, the goal is to move as much of the mobile oil as far into the formation as possible so that the near-wellbore area will be ready for contact with KOH. A water-quality control stations near the injection wellhead can serve as a continuous rate and pressure monitor, as well as a final filtration unit. While the presoak is added, metal surfaces in the system that will be in contact with KOH should be examined. Plastic coatings are suspect unless confirmed to he resistant to highly alkaline potassium solutions. Surfaces should be stainless or plain carbon steel.
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