This paper describes a new water shut-off approach for wells challenged by coning (changed shape of the cone of depression) by injecting the DSGA (Drilling Specialties Gelling Agent) polymer solution with an additional consolidation by cement slurry with improved properties. This approach was implemented at Samotlorskoe Field of TNK-BP Company. This project was implemented as part of pilot works on monolithic and compartmentalized terrigenous formations AV4-5 and BV8(1-3).
The technology deployment scope includes the formations with the system of induced fractures and water breakthroughs, high-permeable interlayers, bottom water, impact of displacement front of injectors. Injection of gel into formation results in a reduced volume of produced water, reduced fluid rate and increased formation drawdown in producers. Injection of gel into formation provides for an increase of pressure gradient between injection and recovery zones and change in direction of in-situ filtration flows. Oil-saturated interlayers of low permeability and watercut previously not covered by displacement are involved in the active reserve recovery process. This results in a reduced volume of produced water, reduced fluid rate and increased formation drawdown in producers.
Increase of well stream watercut is observed in mature fields. This requires deployment of technologies to limit the water inflow. At present, the sources of water inflow are controlled by various technologies — from conventional cementing to use of various mechanical packers and advanced chemicals.
Efficiency of deployed water shut-off technologies can be improved by developing and perfecting the procedures for selection of candidate wells for remedial cementing and also using the holistic execution of works.
Increased of watercut level is caused by several factors such as rise of oil-water contact, inflow of injected and edge water, casing leaks, bottom water coning and crossflows.
The watercut of well stream can be increased due to poor quality of well cementing. In this case a mud cake is formed on borehole walls interfering good adhesion of cement and rock. This mud case is washed away during the well operation that leads to fluid migration between formations.
Use of cement slurries with very low fluid loss can lead to an insufficient dehydration of slurry and consequent low quality isolation of perforations or damage of casing string. Very fast dehydration of the slurry with very high fluid loss can lead to unstable cement not able to withstand pressure drop. Poor quality of cementing results in formation of water and gas fingers during the setting time, improper adhesion of cement and casing string during the cyclic loading, uncontrolled loss of circulation. Fractures are developed in the formation during cement squeezing due to the overpressure. Lack of cement leads to fluid flow, which is aggressive to metal and becomes a reason of through corrosion holes in the casing string. Water entry causes circulation in the casing cement in the points of contact of casing joints with cement and cement with bore wall. Moreover, water ingress may occur due to lost integrity of cement caused by damaged cement plugs and casing leaks.
Typically, integrity of set cement is lost as a result of mechanical damage during tripping, expansion of casing string and compression of cement from pressure tests, expansion and compression of pipes due to cyclic changes of pressure and temperature during well operation. Moreover, integrity of set cement can be damaged by perforation that creates impact loads on casing string.