Optimization Of Volumetric Acid Pressure In Fractured Tight Carbonate Gas Reservoirs

With the gradual reduction of conventional oil and gas resources, unconventional oil and gas has become the focus of the development for petroleum industry, one of which is fractured tight gas carbonate reservoir. By drawing from the thought of stimulated reservoir volume for shale, a pilot test of volume acid fracturing was applied in fractured tight gas carbonate reservoir in China, and has obtained a better effect. Microseismic events have shown that volume acid fracturing create complex fracture network in the reservoir. Compared with the conventional acid fracturing well, the pilot test wells are better in production increase, and have better application prospect. But some people have an unclear understanding of volume acid fracturing implementation conditions in fractured tight gas carbonate reservoir, and the lack of corresponding acid fluid system, and there are some blindness in the selection of process parameters. Consequently, it is necessary to study the feasibility of volume acid fracturing, the corresponding acid fluid system and the selection of process parameters.On the basis of the widespread investigation and study massive literature, this thesis summarized the research status of stimulated reservoir volume thought, numerical simulation of fracture network extension, experiment of acid-etched fracture conductivity in domestic and foreign, and take research on acid fluid system and process parameters of volume acid fracturing. The main research contents are as follows:(1) This thesis analyses the feasibility of volume acid fracturing for fractured tight gas carbonate reservoir from five different aspects:natural fracture development status, rock brittleness, rock fracturing performance, the ratio of the maximum horizontal principal stress to the minimum horizontal principal stress, intersection angle between hydraulic fracture and natural fracture.(2) From the requirement of target reservoir condition and volume acid fracturing technology to acidizing fluid performance, analyzing the composition of acidizing fluid system. And then, the main acid concentration was optimized by static and dynamic dissolution rate experiments, the concentration of resistance reducing agent was preferred by the friction resistance test, the corrosion inhibitor was preferred by the corrosion test of steel sheet, the cleanup additive was preferred by surface tension testing, the ferric ion stabilizer was preferred by the ferric ion contents test and the test of the ability to stabilize ferric ion. Finally, the compatibility experiment was conducted by the optimized main acid respectively with additives and formation water.(3) According to the characteristics of volume acid fracturing, the acid-etched fracture conductivity was measured under the condition of large acid injection rate and large acid doage, the morphology of acid etched fracture was observed, and the effects of acid concentration, closure pressure, acid dosage, acid injection rate, rock plate heterogeneity, surface morphology of acid etched fracture surface and acid fracturing technology on acid-etched fracture conductivity were analyzed.(4) The discrete natural fracture network model and hydraulic fracture propagation model and hydraulic fracture and natural fracture encounter case judgment model collectively form the complex fracture propagation extended model, and use it to optimize fracturing fluid injection rate and dosage during volume acid fracturing. The complex fracture propagation model of volume acid fracturing was created by the complex fracture propagation extended model was coupled with the acid flowing reaction model, and then, through the combination of it and the productivity model, acid dosage is optimized.