Development Of Efficient Shale Gas Reservoir Protection Agent And Study On Its Mechanism

At present, there is a very prominent problem that is water sensitive damage and liquidtrap caused by water-based drilling fluid invasion in the process of shale gas drilling andexploitation, seriously affecting drilling safety and production of shale gas well, even relatedto the value of industrial exploitation of gas wells. Therefore, there is an urgent need todevelop a new type of water-based drilling fluid system that can protect shale reservoirs. Inthis paper, based on the unique properties of the microemulsion, a new type of shale gasreservoir protection agent was developed with the formulation optimization theory. Its shalegas reservoir protection mechanism was revealed, and the drilling fluid reservoir protectiontechnology countermeasures were investigated.With experimental means of X-ray diffraction, scanning electron microscopy, thelow-temperature nitrogen adsorption method, static volumetric method and pulse attenuationmethod, the Shengli oilfield shale reservoir mineral composition, microstructure, physical andchemical properties and potential damage factors were analysed. Studies have shown that thereservoir shale has high clay mineral and brittle mineral content, is compact and accompaniedby many micropores and microcracks whose aperture is nano-level. So it is believed as thelow porosity and low permeability reservoir. Its reservoir characteristics lead to the wellboreinstability. In addition, under the effect of bottomhole pressure difference and capillary forceself-absorption external fluid can be easily penetrated into the reservoir, leading to liquid trap,water block damage, clay particle migration blockage, reservoir permeability decrease, andnot conducive to shale gas output.According to the shale gas reservoir characterization and reservoir damage factor, basedon microemulsion theory and basic reservoir protection principle, two novel microemulsionagents, ME-1and ME-2, were developed by employing Gemini hyamine surfactant GTN,plus Tween80, n-butyl alcohol, n-octane and water as major raw materials. Reservoirprotection behaviors of two microemulsion agents with different concentrations werecompared. Are evaluated various properties of nanoemulsion systems obtained by diluting themicroemulsion agents in different concentrations: surface tension, contact angle, distributionof micelle size, hydration inhibition and spontaneous imbibitions of rocks, permeability recovery tests, and the impact of agents on adsorption characteristics of shale. Because of itsthe best results, ME-2is determined to be the shale gas reservoir protection agent and itsconcentration should be within the range of from0.2%to1.0%. The results have showed thatthe novel microemulsion agent could effectively reduce the surface tension of external fluid,increase contact angle, weaken pore throat shrinkage caused by hydrous swelling, and finallydecrease the capillary pressure of pore throat caused by the incrusion of external fluid uponreservoirs. In addition, micelle could deform and squeeze into micropores, slow downtransmission of pressure and water incursion, and is conducive to wellbore stability. All of theeffects of microemulsion agents can substantially decrease liquid spontaneous imbibition ofrock, recovery low permeability reservoir permeability, and are conducive to shale gasdesorption. The novel reservoir protection agent, ME-2, can be applied in shale gas drilling,completion and fracturing operating fluid.Taking the newly developed shale gas reservoir protection agent as one of primarytreatment agents, a new type of water-based drilling fluid for shale gas reservoir protection,SRPDF system, was developed and its overall performance is good, which has laid thefoundation for field test research in the future.