Research On Limestone Reservoir Characteristics And Reservoir Protection Technology Of Ordovician Yijianfang Formation In Fuyuan-Guole Area

The carbonate reservoir in Fuyuan-Guole area which is the most important reservoir type,but the type of reservoir space is complex and changeable,and in the process of drilling and completion often occurred in the vent,leakage and other accidents,that can easily lead to the external fluid and solid particles into the reservoir damage reservoir,affect the reservoir exploration and development layer.Now,the related research of clastic reservoir damage mechanism and protection technology has been very system.The differences between carbonate reservoir with clastic rocks reservoir of mineral composition and reservoir space characteristics determines its can not follow the evaluation criteria of clastic rocks reservoir.But at present,the research on carbonate reservoir damage mechanism and protection technology is relatively deficient of home and abroad,which requires targeted damage assessment and protection measures based on carbonate reservoir characteristics.Through literature research,this paper compares the differences between the lithology,physical properties and reservoir space characteristics of carbonate reservoirs at home and abroad,and combines the geological characteristics of Ordovician yijianfang formation in Fuyuan-guole area to predict the potential damage factors of the reservoirs.Through indoor evaluation experiments,a reservoir damage mechanism was studied systematically and targeted protection measures were proposed.The specific results are as follows:(1)The reservoir minerals are dominated by calcite,with an average content of about 95%.The porosity is less than 2.5%,the permeability is less than 11.5×10-3?m 2(some samples have microcracking),and the pore permeability correlation is not obvious.(2)There are macroscopic caves,holes,cracks and microscopic pores in the reservoir space.The holes are relatively isolated,the connecting throat is narrow,and there are fewer fillings in the holes.Microscopic pores are dominated by intragranular pores and poor connectivity.The fractures are dominated by structural joints and are mostly half-filled with calcite.According to the combination of holes and seams,reservoir types can be divided into cave type,hole type,fracture type,and crack-hole type,among which cave type and fracture-hole type reservoirs are the main types.(3)According to the loss characteristics of drilling fluid in single wells,the potential damage factors of different reservoir types are predicted by combining the pore structure of reservoirs with the characteristics of sensitive minerals.The main damage factors of cave-type and fracture-hole reservoirs are solid-phase intrusion.(4)About the main reservoir types,such as cave type and fracture-cavity type,the simulation calculation of leakage velocity and fracture width change is carried out,and the mud invasion depth is evaluated by combining with laboratory experiments.The study shows that conventional plugging while drilling and underbalanced drilling can be used to protect the porous reservoirs.For fractured-vuggy reservoirs,reasonable plugging materials should be selected according to the reservoir fracture width and pore development characteristics for shielding temporary plugging.Early completion or pitching plugging techniques can be used for caved reservoirs.