海外岩性油气藏储量分类分级方法

Classification and categorization method of overseas lithologic reservoir reserves

为规范海外石油储量评估,提出海外岩性油气藏储量分类分级、岩性边界、含油面积及有效厚度确定的方法。研究结果表明:①海外P类储量一般必须具有公司或资源国政府批准的开发方案。P1储量以具有商业产量或具商业测试流量的井为计算单元,其面积通常由生产井的泄油面积和已知气底或已知油顶与已知油底限定的范围确定。P1储量边界到其与岩性边界一半距离范围内的储量为P2储量;P2储量边界到岩性边界范围内的储量为P3储量,如圈闭内没有或尚不能确定油水界面,则P3储量应以圈闭溢出点来确定;如岩性或储层物性变化较剧烈,P2储量可按P1储量外推1个开发井距确定,P3储量可按P2储量外推1个开发井距确定。②当P类储量井到渗透储层尖灭线的距离不大于3~4倍开发井距时,对于中—高孔渗储层,尖灭线可直接确定为岩性边界;对低孔渗储层,可将达到P类储量标准的最小有效厚度等值线确定为岩性边界。由岩性边界、油气水边界、致密层封堵带等综合圈定含油气面积,面积内的井应达到P类储量标准。已查明流体界面的油气藏,用于圈定含油气面积的流体界面应经钻井取心资料或测试资料证实;未查明流体界面的油气藏,应以测试证实的最低的出油气层底界或有效厚度值外推圈定含油气面积。③P1储量有效厚度的确定应具有可靠的地层测试资料或充分的测井资料,并证实其具有一定的生产能力;P2储量有效厚度的确定通常缺乏结论性的测试资料,并且未证实其生产能力;P3储量的有效厚度存在较大的不确定性,因其在岩石物理解释方面存在不确定性。④推荐采用容积法开展岩性油气藏的储量评估,厄瓜多尔TP油田的实例证实了岩性油气藏储量分类分级和储量评估方法的有效性。

In order to standardize overseas oil reserves evaluation,a method for classifying and categorizing overseas lithologic reservoir reserves,determining lithologic boundary,o il bearing area and effective thickness was proposed.The results show that:(1)Reserves classified as P generally require a development plan approved by the company or the government of the resources country.P1 reserves are calculated based on wells with commercial production or commercial test flow rates,and their area is usually determined by the drainage area of the production wells and the range limited by the known gas bottom or the known oil top and oil bottom.The reserves within half the distance from the P1 reserves boundary to lithologic boundary are P2 reserves,and the reserves within the range from P2 reserves boundary to lithologic boundary are P3 reserves.If there is no oil water contact within the trap or cannot be determined yet,P3 reserves should be determined based on the spill point of the trap.If there are significant changes in lithologies or reservoir physical properties,P2 reserves can be determined by extrapolating one development well spacing based on P1 reserves,and P3 reserves can be determined by extrapolating one development well spacing based on P2 reserves.(2)When the distance from a class P reserve well to the pinchout line of a permeable reservoir is no more than 3-4 times the development well spacing,for medium to high porosity and permeability reservoirs,the pinchout line can be directly determined as the lithologic boundary,while for low porosity and permeability reservoirs,the minimum effective thickness contour line that can meet the class P reserve standard is determined as the lithologic boundary.The oil and gas bearing area should be comprehensively delineated by lithology boundaries,oil(gas)water contact,tight layer sealing zones,etc,the wells within the area should meet the class P reserve standard.For oil and gas reservoirs with identified fluid interfaces,the fluid interfaces used to delineate oil and gas bearing area should be confirmed by drilling and coring data or testing data.For oil and gas reservoirs with unidentified fluid interfaces,the oil and gas bearing area should be determined by extrapolating the lowest confirmed bottom boundary of the oil and gas producing layer or the effective thickness value through testing.(3)The determination of the effective thickness of P1 reserves should have reliable formation testing data or sufficient logging data and have demonstrated its production capacity.The determination of the effective thickness of P2 reserves usually lacks conclusive testing data and has not confirmed its production capacity.Due to the uncertainty in rock physical interpretation,there is significant uncertainty in the effective thickness of P3 reserves.(4)It is recommended to use the volumetric method for evaluating lithologic reservoir reserves.The application example in TP oilfield in Ecuador has confirmed the effectiveness of the classification and categorization of lithologic reservoir reserves and reserves evaluation method.