Feasibility Study of the In-Situ Combustion in Shallow, Thin, and Multi-Layered Heavy Oil Reservoir

Abstract

Abstract All heavy oil reservoirs in TaoBao oil field are shallowly buried, thin, and multilayered in which natural production and cold production technologies have been implemented in past seven years, and obvious increase in oil production was achieved by cold production(up to 9 times than natural production method). However, due to the low reservoir pressure, heterogeneity, and limited formation thickness, the oil production has rapidly decreased, and more than half of the wells have been shut off now. At present, more than 94% oil remained in place is difficult to exploit, and different recovery methods are being investtigated, as a result, only in-situ combustion is more potential and seems feasible to enhance oil recovery for such reservoir. To investigate the feasibility of in-situ combustion, reactor experiment and combustion tube experiment have been carried out at first, the result shows that the optimal fire temperature is above 400?, and the ultimate oil recovery is more than 80%. Additionally, air injection rate, combustion front velocity and other parameters have been measured or calculated. At the same time, primary reservoir numerical simulation for selected block in Bai 92 reservoir are implemented considering that more importance should be attached to the feasibility of in-situ combustion in reservoir scale. Some important factors such as air injection rate are investigated. Moreover, the progress in pilot test of in-situ combustion in B92 reservoir is introduced briefly. The results of primary experiments, reservoir numerical simulation and pilot test show that in-situ combustion is feasible to enhance oil recovery of such shallow, thin and multilayered heavy oil reservoir as B92. Introduction Bai 92 reservoir is a typical shallow, thin and multi-layered heavy oil reservoir in Jilin Oilfield. The central oil bearing area is about 1.26km2, oil reserve is more than 2,500,000tons. It is a lithologic and anticlinal heavy oil reservoir blocked by a large reverse fault, and there is a large active aquifer in downdip direction. Saertu strata are the oil-bearing sand formation, which consist of 3 stratigraphic units or 16 thin layers with limited thickness (only 2.5m in average), the total thickness of the oil bearing formation is 6.9m in average. The sedimentary environment belongs to braided stream deposit and delta deposit with remarkable heterogeneity in thickness and permeability. The oil-bearing layers are shallowly buried from 272m to 399m. The diagenic metamorphism of the sand deposit is weak, as a result, primary intergranular pore and dissolution pore is dominant there, unconsolidation of intergranular cement generated, and higher porosity and permeability observed in core analysis(average porosity is up to 35%, and average permeability 3600×10–3µm2). As a whole, the formation is strong in water sensitivity, flow rate sensitivity and alkaline sensitivity. Under reservoir condition(18 and 3.22MPa), the oil density is 903.8kg/m3, viscosity 1.851Pa·s, ratio of separated gas to oil 10.2m3/m3, volume ratio of crude oil 1.03, and saturation pressure 3.2MPa close to initial reservoir pressure.