鄂尔多斯盆地大牛地气田致密砂岩气藏水平井压裂“甜点”识别方法

Horizontal well fracturing“sweet spots”identification method for tight sandstone gas reservoir in Daniudi Gas Field in Ordos Basin

大牛地山西组致密砂岩储层非均质性较强,凭借岩心、测井、录井资料等常规预测手段识别压裂“甜点”效果不理想。为了精确水平井压裂选段,提高压裂改造效果,在明确影响压裂甜点的地质、工程参数基础上建立测井解释模型,而后优选熵值分析法明确了各参数对压裂效果的影响程度,最后利用综合权重法建立压裂“甜点”计算模型。结果表明:校准后的储层参数测井解释模型预测精度提高了37.2%~46.3%;孔隙度、渗透率、弹性模量、泊松比4项参数是影响大牛地气井压裂效果的关键因素,参数累计权重所占比例高达53.32%;依据单井压裂“甜点”识别结果,明确了最佳压裂“甜点”位置与非压裂“甜点”位置,经过产气剖面数据验证,压裂甜度与单段产气量具有良好的正相关关系。矿场13口井压裂数据表明,应用此压裂“甜点”预测方法得到的甜度与压裂后产能的相关度达85.2%,此方法可为提高致密砂岩气藏水平井压裂效果提供技术支撑。

High heterogeneity of the tight sandstone reservoirs of Daniudi Shanxi Formation leads to uneffective identification of sweet spots by means of conventional prediction methods using cores,geophysical logging and mud logging data.In order to accurately select fracturing intervals of horizontal wells and improve stimulation effect,logging interpretation model is established firstly through clarifying geological and engineering parameters affecting fracturing sweet spots.Then entropy analysis method is optimized to clarify the influence degree of each parameter on fracturing effect.Finally,fracturing“sweet spot”calculation model is established by comprehensive weight method.The results show that prediction accuracy of calibrated logging interpretation model of reservoir parameters increases by 37.2%~46.3%.Porosity,permeability,Young's modulus and Poisson's ratio are the key factors affecting fracturing effect of Daniudi gas well,with cumulative weight accounting for 53.32%.Based on the identification results of single well fracturing“sweet spots”,the optimal fracturing“sweet spots”position and non‑fracturing“sweet spots”position are determined,and gas production profile data verifies good positive correlation between fracturing sweetness and single‑interval gas production.In addition,evaluation and analysis of fracturing“sweet spots”of 13 field wells show that the correlation between sweetness value and post-fracturing productivity reaches 85.2%.This method provides technical support for improving the fracturing effect of tight sandstone gas reservoir horizontal wells.