Drilling Fluid Technology For Igneous Reservoir Protection In SCWS Block

As the main body of the three lithology,igneous rock is low in oil and gas resources and has broad exploration prospects.Igneous reservoir structure is complex,and its development is difficult.Igneous rock in SCWS block is a special reservoir with low permeability and fracture.It is easy to cause reservoir damage during drilling,and the field drilling fluid can not meet the requirements.Therefore,this paper aims at the study of igneous reservoir damage mechanism and the construction of reservoir protection drilling fluid in this block.Analyzes its potential damage factors through a variety of experimental means,determines the main damage types of the reservoir,reveals the damage mechanism,researches and selects the key treatment agents suitable for the reservoir,and constructs the igneous reservoir protection drilling fluid system in SCWS block.The analysis results of mineral composition,microstructure and pore permeability structure parameters show that the main mineral components of igneous reservoir in SCWS block are plagioclase,calcite,quartz and clay.The content of chlorite in clay mineral is high,and it is easy to cause particle migration damage because it is filled in pores.The development of microfracture in reservoir rock is easy to cause solid invasion damage.The pore throat of reservoir rock is small,and the maximum pore throat is half the diameter is3.78μm,the heterogeneity of pore throat is strong,and the seepage capacity is poor,which is easy to cause damage to liquid traps.The sensitivity test results of normal temperature and high temperature and high pressure show that the damage types and degrees of the block are strong hydrochloric acid sensitivity（damage rate is 80.4%）and stress sensitivity,medium weak water sensitivity（damage rate is35.1%）,alkali sensitivity（damage rate is 18.7%）and salt sensitivity（damage rate is 37%）.The critical velocity of gas and liquid is 4.03 m L·min^-1.Through the analysis of the microscopic mechanism of particle migration by nuclear magnetic resonance T₂ monitoring technology,it is found that in the process of particle migration,the pores are blocked or divided into more small holes,resulting in the further enhancement of pore heterogeneity;through the single core and double core flow blocking experiments,the compatibility test of particle size and core pore throat,and CT scanning technology,the types of particle damage are clarified:when the injection concentration is low,the particle size is high.And the pore throat is low.When the particle size and concentration increase,the particles are mainly deposited in the surface pores.The cumulative permeability damage rate is as high as 68.5%.The matching relationship between particles and pore throat is quantified,It is found that when the ratio of particle size and pore throat diameter is 0.25-0.5,the particle migration causes serious damage to the core,and the porosity is reduced by 63.7%at the highest;the self absorption and core displacement experiments are used to evaluate the reservoir water lock damage.The external fluid is easy to self absorb and stay in the pores and micro fractures,and the water lock damage is more serious.In view of the above damage factors and damage mechanism,the paper proposes the igneous reservoir protection countermeasures based on temporary plugging and film-forming,strengthening plugging,inhibition,waterproof and locking performance,prepares the temporary plugging and film-forming agent suitable for the reservoir in this block,forms a dense‘accumulation film-forming barrier’near the well zone,and constructs a set of reservoir protection drilling fluid with good performance combined with the optimization of waterproof and locking agent and other treatment agents the core permeability recovery rate is 86.92%,which can play a good role in reservoir protection during drilling.