咸化湖盆致密油储层“甜点”预测方法研究:以柴达木盆地扎哈泉地区上干柴沟组为例

The prediction method of the tight oil reservoirs “sweet spot” in saline lacustrine basin:A case study of the upper Ganchaigou Formation in the Zhahaquan district of Qaidam Basin

柴达木盆地致密油勘探起步较晚,但勘探潜力巨大。扎哈泉地区上干柴沟组致密油储层受咸化湖盆的影响,砂体单层厚度薄,纵向上叠置明显,侧向变化快,储层"甜点"预测是研究的重点和难点。地震沉积学在沉积体系研究和薄层砂体预测中扮演着重要作用,文中以地震沉积学思想为指导,利用相位转换、地层切片、定量地震沉积学等技术,在建立高分辨率层序地层格架的基础上,开展了扎哈泉地区上干柴沟组4个准层序组砂体的地震沉积学研究,并结合钻井、测井等资料对典型地层切片进行了精细地质解释与标定,预测了不同沉积时期薄层滩坝砂体的分布和演化。研究表明:研究区主要以滨浅湖相沉积为主,滩坝砂体分布广泛。在分析致密油储层性能主控因素基础上,提出利用伽马反演技术可预测储层"甜点"的分布,并指出了有利勘探区,预测结果与实际钻井吻合程度高,有效指导了研究区致密油勘探,并对其他有类似地质特征的地区储层预测具有借鉴意义。

Tight oiI exploration in Qaidam Basin started relatively late, but with great potential. Under the influence of saline lacustrine basin, the tight oil reservoir of the upper Ganchaigou Formation in Zhahaquan district is characterized by thin single layer, distinct vertical overlap and significant lateral change, and thus the prediction of reservoir sweet spot has become the key and difficult point in this research. Based on the established high resolution sequence stratigraphic framework and the application of phase inversion, of strata slicing and of quantitative seismic sedimentology techniques, the seismic sedimentology study was conducted on the sand bodies composed of four parasequence sets in the upper Ganchaigou Formation, Zhahaquan district with the guidance of seismic sedimentology, which plays an important role in the deposition system research and thin layer sandstone prediction. Furthermore, combined with drilling and logging data, typical strata slices were precisely interpreted, as well as calibrated, and the distribution and evolution of thin beach bar sand bodies was predicted. This research suggests that shore-shallow lacustrine facies was dominated in the study area, where beach bar sand bodies were widely distributed. Also, on the basis of controlling factors analyses on tight oil reservoir performance, gamma inversion technique was proposed for prediction of reservoir sweet spot, and the favorable exploration area was determined. In addition, the prediction results tallied with the actual drilling situations, which effectively guided tight oil exploration in the study area and can be applied to prediction of reservoirs with comparable geologic characteristics in the future.