南海北部白云深水区高变地温梯度砂岩渗透率定量预测

Quantitative Prediction of Permeability of High Variable Geothermal Gradient Sandstone in Baiyun Deep Water Area of Northern South China Sea

地温梯度如何影响砂岩成岩演化和储层物性变化是地学界的热点问题.以具有高变地温梯度特征的白云深水区为例,通过分析大量不同地温梯度地区的样品,以地温梯度0.1~0.2℃/100 m为递进间隔,对比分析了不同地温梯度区间内不同粒度砂岩储层渗透率随埋藏深度变化的趋势,建立了砂岩渗透率的定量地质预测模型,展示了砂岩渗透率与地温梯度之间的内在联系.结果表明,一定埋深范围内,随地温梯度升高,渗透率每下降一个数量级,砂岩埋深下限差异呈台阶式减少;相同地温梯度区间内,高成分成熟度、低塑性岩屑含量的含砾砂岩、粗粒砂岩、中粒砂岩和细粒砂岩的渗透率下降程度不同,相邻粒径砂岩等效渗透率埋深下限差异相近,随地温梯度增加,相邻粒径砂岩等效渗透率下限埋深差异呈规律性减小;低渗与特低渗砂岩储层的地层深度段随地温梯度升高而明显变小,粗粒砂岩特低渗储层的埋深下限可作为白云深水区常规油气勘探的极限深度.研究成果对于揭示地温梯度对砂岩成岩演化作用的影响及物性演变效应具有重要的意义,对油气勘探有积极的指导作用.

How the geothermal gradient affects the diagenetic evolution of sandstone and the change of reservoir physical properties is a hot issue in the field of geosciences.Taking the Baiyun deep water area with a highly variable geothermal gradient distribution as an example,through the analysis of a large number of samples from different geothermal gradient areas,with a geothermal gradient of 0.1 °C/100 m as the progressive interval,in this paper it compares and analyzes the variation trend of the permeability of sandstone reservoirs of different grain sizes with burial depth in different geothermal gradient intervals,establishes a quantitative geological prediction model of sandstone permeability and shows the inherent relationship between the reservoir properties of sandstone and the stratum geothermal gradient.The results show that within a certain buried depth range,with the increase of geothermal gradient,the difference of lower buried depth decreases step by step with the decrease of permeability by an order of magnitude.In the same geothermal gradient range,for pebbly sandstone,coarse-grained sandstone,medium-sized sandstone and fine-grained sandstone with high composition maturity and low plastic debris,the difference of lower limit of equal permeability between adjacent grain size sandstones is similar.With the increase of geothermal gradient,the difference of lower limit of equal permeability between adjacent grain size sandstones decreases regularly.The thickness of low permeability and ultra-low permeability sandstone reservoirs decreases with the increase of geothermal gradient,and the ultra-low permeability lower limit of coarse-grained sandstone can become the limit depth of deepwater conventional exploration.This study has important scientific significance for revealing the influence of geothermal gradient on the diagenetic evolution of sandstone and physical property evolution effect,and has a positive guiding role for oil and gas exploration.