混合润湿致密砂岩颗粒表面形貌特征及其影响天然气运移与聚集机理的研究

The gas from tight sandstones is an important natural gas source that growing in reserves and production in China. But there is an obscure comprehension in the mechanism of gas migration and accumulation in the tight sand reservoirs, which seriously restricts the exploration progress and effectiveness of these gas resources. Our previous works have proved that the mixed wetting pores composited with oil-wet and water-wet pore-throats obviously diminish dynamic for oil and gas migration, and the impact of porosity and permeability becomes weaker than wettability. This conclusion has an especially critical significance in migration and accumulation for hydrocarbon in the reservoirs with poor qualities. We select the Dibei gas reservoir, which locates in Kuqa Depression of Tarim Basin and experienced an early oil emplacement, as the target to recognize the mechanism. We firstly investigate the framework grain microtopography difference from various wettability sandstones to illuminate the reason for the microtopography influencing the micro-percolation dynamics of gas by the techniques of wettability determination and microtopography deconstruction. Secondly, the flowing pattern, dynamic, micro-pathways and accumulation occurrence for gas in the tight sandstones with mixed wettabilities will be researched by percolation experiments, such as spontaneous imbibition and gas displacement in high temperature and pressure, which all integrated with measurement and imaging from nuclear magnetic resonance, to determine the effects of oil-wet pore-throats on the gas flowing and retention. At the last, the relationship between oil-wet index and gas saturation and the main factors controlling oil-wet pore-throats will be analyzed to reveal the idea for predicting sweet spots in the tight sandstones with mixed wettability. The results and conclusions from this applying research would reinforce the understanding on the forming of gas accumulation, broaden the prediction fields for sweet spots in gas production and enhance the drilling rate in tight sandstones, if it was conducted. The application prospect in the exploration for tight sand gas is extremely wide.

致密砂岩气是我国天然气资源增储上产的重要领域，但目前对致密砂岩气运聚机理的认识仍不明确，制约了勘探进展。我们前期研究证实，亲油和亲水孔喉共存的混合润湿孔隙明显降低了油气运移所需的动力条件，物性所起作用减弱，这对致密储层中油气运聚的意义重大。本项目以经历过早期石油充注的迪北气藏为研究对象，利用润湿性测定和形貌解构技术比较不同润湿性致密砂岩颗粒表面微观形貌的差异以阐明其影响天然气微观渗流力学状态的机理；通过自动渗吸和高温高压气体驱替实验，结合核磁共振成像技术研究混合润湿砂岩中气体渗流方式、动力、通道和赋存状态以明确亲油孔喉在天然气运移和聚集过程中的作用；通过实际混合润湿气藏验证亲油指数和含气性的关系，明确亲油孔喉发育的主控因素，提出混合润湿致密砂岩储层含气甜点的预测思路。本项目的研究将深化致密砂岩气成藏理论的认识，拓宽含气甜点的预测领域并提高钻井成功率，在致密砂岩气勘探领域的应用前景十分广阔。

致密砂岩气是我国天然气资源增储上产的重要领域，岩石颗粒表面润湿性直接影响流体渗流，然而混合润湿致密砂岩储层内天然气运移和聚集机理的认识仍不明确，严重制约了致密砂岩气勘探成效和进展。本项目聚焦混合润湿致密砂岩颗粒表面形貌及其影响气相流体运聚的问题，采用岩石表面微观形貌解构和渗流实验的研究方法和技术，开展了混合润湿性砂岩颗粒表面微观形貌特征、混合润湿致密砂岩中气相流体渗流行为及赋存状态和实际混合润湿致密砂岩气藏含气性验证的研究内容，取得的主要成果包括：1）库车坳陷迪北地区下侏罗统阿合组致密砂岩储层相对润湿指数为-0.22~0.82，亲油和亲水同时存在的混合润湿状态约为40%，说明混合润湿状态较普遍；2）致密砂岩储层的混合润湿的形成与岩石颗粒表面粗糙程度差异相关，光滑表面表现出亲水性，粗糙表面表现为亲油性；3）岩石颗粒表面形貌的变化受矿物组分和早期液态烃类的双重影响，粘土矿物包膜与极性分子增强颗粒表面粗糙度；4）岩石颗粒亲油表面对水相流体的粘滞力变弱，混合润湿孔隙介质减小天然气发生渗流的动力阀值，气相流体更容易发生运移；5）迪北地区致密砂岩储层在混合润湿状态下自生伊利石化程度相对减弱，含气饱和度相对增大，说明混合润湿改善储层物性和油气富集条件。项目研究成果及认识加深了对天然气运聚成藏理论和致密砂岩气成藏模式的理解和把握，拓宽了致密储层含气甜点区勘探领域。