Inhibitor For Shale Gas Wells And Wellbore Stability Water-Based Drilling Fluid

In order to solve the problem of wellbore stability during the drilling of shale gas wells,researchers at home and abroad have carried out a large number of anti-collapse drilling fluids.Both domestic and foreign scholars agree that sodium silicate drilling fluid is one of the most promising water-based drilling fluid systems.However,the sodium silicate drilling fluid has many problems,such as the control of rheology,the weakened inhibition performance of sodium silicate in strong alkaline conditions and so on.Therefore,the system was limited on the application in the oil field.In this paper,sodium silicate?modulus 3.3?and tri-chain sodium methyl silicate were used as high-efficiency shale inhibitor for drilling fluid,and a drilling fluid system was constructed.Through the study of the hydration inhibition performance of sodium methyl silicate with different chain lengths,it was proved that sodium trisodium silicate has strong hydration inhibition performance.The mechanism of the collapse is that tri-chain sodium methyl silicate can be adsorbed on the surface of clay particles to reverse the wettability of the shale surface,thereby inhibiting the hydration of shale;through the study of sodium silicate hydration inhibition performance,it was proved that the sodium silicate?modulus 3.3?has strong hydration inhibition performance.The mechanism of the collapse is that the smaller particle size of the sodium silicate aggregates can enter the shale formation pores which react with Ca²⁺to form larger aggregates and then block the shale pores as Na⁺could replace Ca²⁺in alkaline condition;based on the analysis of the mechanism of the collapse of tri-chain sodium methyl silicate and sodium silicate?modulus 3.3?,the synergistic mechanism of high-efficiency shale inhibitor in hydration inhibition performance was discussed..Studies have shown that unhydrated clay,calcium ions and neutral or acidic fluid in shale all contribute to the rheological instability of the sodium silicate drilling fluid.The feasibility of the weak acid salts and tri-chain sodium methylsilicate as flow regulators for sodium silicate drilling fluid was studied experimentally.The study found that the flow adjustment effect of tri-chain sodium methyl silicate is much better than that of various weak acid salts,and the mechanism of the flow adjustment of tri-chain sodium methyl silicate was emphatically analyzed.A water-based drilling fluid formula for shale gas wells was developed based on high-efficiency shale inhibitor.The formula is as follows:4%slurry+5%sodium silicate?modulus 3.3?+5%tri-chain sodium methyl silicate+0.3%CMC-HV+0.3%CMC-MV+1%SLR-2.The properties of drilling fluid were measured such as temperature resistance,hydration inhibition,anti-bentonite and anti-inorganic salt performance.The experimental results show that the system has good resistance to temperature,anti-temperature up to150?;the system has strong hydration inhibition performance,clay linear expansion rate of only 4.5%;the system has good anti-bentonite pollution ability,anti-bentonite up to 10%;the system has good resistance to inorganic pollution,resistance to NaCl pollution up to 10%,anti-CaCl₂ pollution up to 1.5%.