Study On Protection Technology Of Underbalanced Drilling Reservoir In Block Of Xujiahe Formation In Heyue And Hechuan Block

In recent years, more than200wells has been drilled to use underbalanced drilling technology in the Chuanzhong clastic rock reservoir, it plays an important role in the discovery and protect reservoir. Because the underbalanced wells are generally low of the production, and it doesn’t give full play to its advantages in protecting reservoir and improving the effect of single well production.The number of underbalanced wells reduced year by year. To solve this problem,the paper studies in based on the Xujiahe formation of the Anyue and Hechuan areas.First the characters of Xujiahe reservoirs are investigated,then based on the research of formation damage,the paper carried out research and analysis of potential geological damage factors,the type of damage,and studied the damage under the condition of underbalanced,which includes geological damage factors,the type of damage,and conventional completion damage. Based on the above analysis,the paper put forward a series of underbalanced drilling technical measures for protecting reservoir,and the test of underbalanced application was conducted in the Yue101-88-H2well and Hechuan001-55-X2well.After the systematic studies,the paper gets the following main results:(1)Through studying the primordial data and observing the core, the paper analyzes the basic geological characteristics of the Xujiahe reservoir Anyue and Hechuan block,which includes rock characteristics,reservoir space,reservoir characteristics. According to the geological characteristics,it analyzes the potential damage factors and damage type of the reservoir.(2) Based on the research of formation damage, the paper carried out research and analysis of potential geological damage factors and the type of damage. The result shows that there are middle to serious water-sensitive, weak gas velocity sensitive, serious water phase trapping, middle to serious acidulous sensibility,serious stress sensibility.(3)Laboratory experiments were analyzed to study the reservoir damage under different negative differential pressure, different crack width, different drilling fluid systems and underbalanced drilling®ular completion. The result shows that underbalanced drilling has good effect on the protection of tight sandstone reservoir, and fractured reservoir is more vulnerable to damage than porosity reservoir.The damage of underbalanced drilling and regular completion is more serious than underbalanced drilling.(4) Combined with underbalanced drilling application of the Xujiahe formation Chuanzhong reservoir,the paper summarizes the underbalanced drilling application effect, and qualitative analysis was carried out about the underbalanced drilling reservoir damage factors.The conclusion is obtained which reveals poor performance the reason of underbalanced drilling in protecting reservoir and improving the single well production. The reasion includes:①Exploratory well ratio is high, the production is uncertain;②Vertical well is the main well type;③The negative differential pressure design is not reasonable;④The whole process underbalanced drilling application well number is less, so much so that reservoir protection is not enough.(5) Depending on the type of reservoir damage and damage mechanism, the paper puts forward a set of protecting reservoir of underbalanced drilling technology ideas and measures in the Xujiahe reservoir Anyue and Hechuan block.which includes well and layer optimization,negative differential pressure optimization design,drilling fluid optimization, underbalanced completion method optimization and fracturing fluid optimization. The field tests were conducted in the Yue101-88-H2well and Hechuan001-55-X2well, and it achieved good results in the protecting reservoir and increasing production of signle well.The application case proves that the protection technology is effective.