大港深层低渗油藏孔隙结构特征及动用潜力评价

Pore structure characteristics and development potential evaluation of Dagang deep low permeability reservoir

基于大港深层低渗储层岩样,开展恒速压汞、纳米CT、高速离心和核磁共振(nuclear magnetic resonance,NMR)实验,研究储层孔隙结构特征及动用潜力。研究结果表明:1)喉道发育的好差与渗透率呈较好的正相关性,渗透率较大时,喉道半径、喉道体积均较大,喉道个数较多,喉道发育较好,反之亦然。2)渗透率大于3 mD储层有效喉道半径大于2μm,喉道半径和体积较大,喉道个数较多,微米孔喉占比约为40%。3)渗透率小于1 mD储层有效喉道半径和体积均明显小于其他储层,喉道个数最少,微米孔喉占比小于20%,喉道发育程度最低。4)纳米CT表明,渗透率大于3 mD储层局部发育联通性较好的大喉道,渗透率小于1 mD储层的孔喉尺寸较小,联通性差;渗透率大于3 mD储层平均喉道半径和喉道体积分别为3.61μm和61.56×10^(6)μm^(3),远高于渗透率为1 mD以下储层。5)渗透率大于3 mD储层的可动流体高,微米喉道控制占比接近40%,开发潜力较大;渗透率为1~3 mD储层可动流体大于50%,微米喉道控制占比大于20%;渗透率为0.5~1 mD储层微米喉道控制占比约为10%;渗透率小于0.5 mD储层总可动流体低,且主要被亚微米、纳米喉道控制,储层开发潜力较差,且开发难度较大。6)渗透率大于3 mD储层微米孔喉占比接近40%,渗透率为3 mD时岩心T2谱左右峰比例相当,亚微米以上喉道控制的可动流体量大于50%,渗透率为3 mD可以作为目标油藏水驱动用的渗透率界限;渗透率小于1 mD储层微米喉道占比很低,可动流体量很少,常规水驱不能实现油藏的有效动用,需探索其他开发方式进行开发。

Based on the rock samples of Dagang deep and low permeability reservoir,constant velocity mercury injection,nano CT,high-speed centrifugation and nuclear magnetic resonance(NMR)experiments were carried out to study the pore structure characteristics and development potential.The results show that there is a good positive correlation between the development degree of throat and permeability.When the permeability is large,the effective throat radius,threshold pressure throat radius and effective throat volume are large,the number of effective throat is large,the development degree of throat is high,and vice versa.The effective throat radius of core larger than 3 mD is larger than 2μm,and the proportion of micro pore throat is about 40%.The proportion of micro pore throat in core less than 1 mD is less than 20%,and the development degree of throat is obviously the lowest.Large throat with good connectivity is developed locally in core larger than 3 mD,while small pore throat size and poor connectivity are developed in core smaller than 1 mD.There is a good positive correlation between the movable fluid and the permeability.The average of the movable fluid in the target reservoir is about 55%.The total movable fluid in the reservoir larger than 3 mD is relatively high and the control proportion of micro throat is close to 40%,which indicating the development potential is large.The total movable fluid of 1-3 mD reservoir is more than 50%,and the control proportion of micro throat is more than 20%.Less than 1 mD reservoir has low total movable fluid and is mainly controlled by submicron and nanometer throat,so the development potential is poor and the development is difficult.The proportion of micro pore throat is high in the reservoir larger than 3 mD,and the amount of movable fluid controlled by micro pore throat is more than 50%.Therefore,3 mD can be used as the limit of water drive in the target reservoir.The proportion of micro throat is low and the amount of movable fluid is small in the reservoir less than 1 mD.Conventional water flooding could not achieve effective production of this kind of reservoir,so it is necessary to explore other methods for development.