Polymer Gel Squeeze for Gas Shutoff, Water Shutoff and Injection Profile Improvement in Bombay High Pilot Wells

Abstract

Abstract In heterogeneous stratified reservoirs with low vertical communication between the layers, the best results are normally achieved if the separate layers are produced with a separate set of Wells. However, in a commingled production with poor vertical sweep due to high permeable thief zones, an improved behavior of such a reservoir can be efficiently attained by controlling the injection and production rates of wells to reduce (or stop) injection in the thief zones, and/or production from high permeable layers with high water cut. Technically this can be done by recompletion of wells or with the application of gel technology. The problem high GOR & high water cut wells of Bombay High L-III reservoir can be classified into three categories:Wells producing high amount of gas &/or water due to hardware leak and flow behind casing. The unwanted gas/water production here is due to contribution from zones not opened/exposed for production.Wells producing from multiple layers and a single layer producing major amount of gas or water. The unwanted water production may be due to breakthrough of injection water in one or more high permeable layers. The unwanted gas production may be due to cusping.Wells where early breakthrough has occurred due to thin high permeability streaks in a sublayer between Injectors and Producers. Here, the treatment may involve treating a portion of sublayer. In the past several Chemical water shutoff jobs in Bombay High Field have resulted in failures. The job failure can mainly be attributed to high reservoir temperature and incompatibility of Gel system with reservoir rock. Gel systems were quite sensitive to variations in temperature and pH. Also cross flow in the well bore during shut in conditions was also an important reason in some cases. An improved polymer gel treatment has been successfully applied in Bombay High Field - a high temperature carbonate reservoir, to control excessive gas or water production and to modify the injection profiles. Ten Wells were treated as a pilot: 6 for Gas Control, 3 for Water Control and 1 for Injection Profile Improvement. All the planned wells exhibited at least one, usually more than one, of the following conditions: At least one interval with vuggy porosity, poor primary cement over at least a portion of pay, additional loss of rock volume due to acidization, reservoir pressure less than hydrostatic in producing wells, differential pressure between zones due to differential depletion or water flood support. This paper discusses in detail the lessons learnt from the job failures and the successes with the use of polymer gels in such harsh conditions of Bombay high field. Introduction Bombay High, a giant oil field discovered in 1974, is located 160 km offshore WestNorthwest of Mumbai in Arabian Sea. Hydrocarbons have been found in Limestone, clastic and basement in the intervals -905m to -1950m MSL. It has two main limestone reservoirs of Miocene age, namely L-II and L-III. L-II reservoir is hydrocarbon bearing in Bombay High North (BHN) and L-III is hydrocarbon bearing in both Bombay High North and Bombay High South (BHS). The hydrocarbon accumulation is largely controlled by the structure which is a broad North-South trending anticline with a large portion of the eastern limb truncated by the eastern boundary fault (Figure: 1). The L-III reservoir is multilayered with shale, limestone sequence and hold about 94% of the total initial oil in place and reserves. The northern and southern parts of Bombay High field are hydrodynamically separated by an East-West trending shale channel in L-III reservoir, with perceptible difference in gas-oil contact level in L-III, in the north and the south Bombay High1.