On The Reservoir Fluid Pressure Condition Rock Mechanics Parameter Test Method

Coal reservoir and conventional reservoir in coal rock lower elastic modulus,high Poisson's ratio,lower compressive and tensile strength,brittleness,and coal structure heterogeneity,the development of primary and secondary fissure system,coal rock is compressed and broken more easily than conventional rock in coal reservoir in the process of drilling stress changes easily induced collapse.Researchers at home and abroad in order to solve the coal reservoir drilling borehole stability problems,research methods from the early coal reservoir,wellbore stability of theoretical mechanics to indoor rock mechanics experiment now have done a lot of work,theoretical mechanics tends to improve,however,indoor simulation of coal reservoir,determination of drilling parameters of rock mechanics conditions there are many defects in simulation conditions,resulting in inaccurate measurement data,CBM drilling fluid development direction is not clear.Through a large number of literature research to determine the main controlling factors of borehole stability in the process of coal and rock reservoir drilling,mainly divided into:the main geological factors,the main control factors of drilling fluid,the main control factors.The main geological controlling factors are structural characteristics,rock characteristics,mineral composition,methane desorption,fracture development and so on.The main controlling factors of drilling fluid are drilling fluid density,drilling fluid filtrate and so on.Engineering master elements are drilling pressure,impact drill bit excited.These factors are related to the selection of rock mechanics test conditions.Optimization of water drilling fluid,polymer drilling fluid,special anti sloughing drilling fluid gas soft capsule as the control,making artificial coal rock core,choosing suitable confining pressure and test process of three axis rock mechanics test of fluid under the new conditions,obtained with the conventional method are more close to the real coal reservoir drilling the data also proved that this method is feasible.Through the analysis of test data with three axis rock fluid mechanics conditions that:(1)water drilling fluid anti sloughing mechanism by K~+ion suppression of clay mineral swelling collapse prevention,but coal still exhibits brittle;(2)polymer anti sloughing drilling fluid special anti sloughing mechanism is formed through the outer sealing mud cake isolation of the drilling fluid and the coal matrix contact at the same time,the mud cake can improve the mechanical strength of the coal matrix;(3)soft capsule drilling fluid gas anti sloughing mechanism through soft capsule self matching sealing drilling fluid and isolation of coal matrix contact,also is the velvet bag storing coal matrix from brittle to plastic to reduce the impact of drilling process,drilling pressure generated excited stress sensitivity to anti sloughing.