Research On The Physical Properties And Percolation Mechanism Of Tight Sandstone Reservoir In Daqing Oilfield

Taking tight sandstone reservoir in Daqing peripheral area as research object,research on porosity and permeability property under the overburden pressure was conducted by porosity and permeability test.By using constant-pressure and constant-rate mercury injection methods,the pore structure features of Fuyu and Gaotaizi tight reservoir were studied.Besides,comparative analysis is conducted on percolation characteristic of tight sandstone matrix cores and fracture-matrix cores.Based on dynamic imbibition theory,dynamic huff-puff imbibition physical simulating experimental method and device were established,which is applicable to high temperature and high pressure conditions of tight reservoir,and research on effects of different factors on huff-puff imbibition recovery was conducted.The achievements show that:(1)The data of porosity and permeability under normal pressure show that the porosity and permeability condition in Fuyu reservoir is better than that in Gaotaizi reservoir.With increase of effective overburden pressure,the porosity and permeability of matrix cores gradually increase,and the loss rate of porosity is significantly lower than that of permeability;to fracture-matrix dual media cores,the loss rate of permeability under constant effective overburden pressure is lower than that of constant displacement pressure,increase of pore pressure can maintain fracture opening and reduce damage level of stress sensitivity.(2)Contribution to permeability of tight sandstone cores mainly comes from pores at submicron scale.Compared with Fuyu reservoir cores with same permeability,Gaotaizi reservoir cores have characteristics as follows: the development degree of pore throats and pores is relative weaker,radii of pore throats have smaller ranges,higher displacement pressure,capillary pressure curves have smaller slanting degrees.The permeability of tight sandstone cores is positively linear with average radius of pore throats and highest throat radius,with increase of permeability,sorting becomes poorer.(3)To porous media of tight sandstone reservoirs,there are apparent non-linear features in water phase flow and oil phase flow under irreducible water condition,the threshold pressure of oil phase is obviously higher than that of water phase.To matrix cores,the oil-water relative permeability curves shows that: irreducible water saturation and residue oil saturation are relatively high,the scope of oil-water phase co-permeance scale is narrow,the water phase relative permeability under residue oil saturation and the relative permeability of equal-permeability point are both low.In the process of water flooding,sustaining liquid producing is not enough to achieve stable development.Compared with matrix cores before fracturing,the fractured cores have a wider scope of oil-water phase co-permeance scale,its displacement efficiency rises faster,and the final displacement efficiency increase.(4)With increase of permeability or reservoir temperatures,the huff-puff imbibition recovery of tight sandstone increases;with increase of oil-water viscosity ratio or volume-surface ratio,the recovery decreases;the recovery of the oil wet cores is lower than that of water wet cores which are similar in porosity or permeability degrees;the existence of fracture makes the recovery increase;under the control of imbibition replacement effect,with increase of production pressure,the recovery changes insignificantly,but the efficiency of flow-back process increases.Taking active water as imbibition media,the imbibition recovery is higher than that of clean water,the imbibition recovery of clean water is also higher than that of formation water,as the filtrated guar fracturing fluid is harmful to reservoir,its imbibition recovery is relatively lower.