Analysis of coal reservoir sensitivity and compatibility in Junlian Area

Reservoir sensitivities，including velocity sensitivity，water sensitivity，salt sensitivity，acid sensitivity and stress sensitivity (five sensitivities)，directly affect the fluid selection and coalbed methane production in the process of drilling，fracturing and other engineering processes. In order to find out the coal reservoir sensitivity and fluid compatibility，samples of C2+3 and C7+8 coal seams of Permian were collected，and the characteristics of porosity and permeability were analyzed by low temperature liquid nitrogen adsorption and nuclear magnetic resonance. On this basis，five sensitivities test were carried out through core flooding，and the compatibility of formation water and fracturing fluid in different wells was studied. The results showed that the coals are mainly semi dull coal，medium to high ash content，with the vitrinite reflectance being higher than 2.2%. There are few seepage pores in the coal，and the pore types are mainly adsorption pores. Micropores and mesopores are dominant，and the connectivity between micro-meso pores and macropores is poor. The average specific surface area of coal is 4.55 m2/g and the average total pore volume is 0.004 9 mL/g. Focusing on samples from JL-1 and JL-2 wells，the velocity sensitive damage ratio is 20.74% and 25.26%，with the water sensitive damage of 12.52% and 19.29%，salt sensitive damage of 14.68% and 19.84%，acid sensitive damage of -0.077% and -0.057%，and stress sensitive damage of 76.82% and 47.67%，respectively .According to the standard of SY/T 5358—2010，the coal reservoir shows weak velocity sensitivity，weak water sensitivity，weak salt sensitivity and no acid sensitivity，while shows medium weak and strong stress sensitivity. After filtering formation water and fracturing fluid，the turbidity was measured by mixing them in different volume proportions (0∶1，1∶1，1∶2). The overall compatibility of fracturing fluid and formation water was good，the turbidity was clear，and there was no precipitation. The relevant results provide scientific basis and technical support for identifying the influencing factors of coal reservoir sensitivity and guiding the follow-up fracturing construction.