深部碳酸盐岩油气储层原位溶蚀模拟实验研究

Deep carbonate reservoirs are important targets form hydrocarbon exploration. However, the formation of the dissolution pores of these reservoirs is one of the major point of debate, as well as a key problem for reservoir prediction. Former researchers have done many experiments on carbonates dissolution. Nevertheless, this problem is far beyond dissolved. This research will firstly establish a theory model for dissolution based on thermodynamic calculation, and a geological model for dissolution based on the typical carbonate reservoirs from the Sichuan Basin and the Tarim Basin. And a new set of experimental apparatus is designed which is mainly composed of Diamon Anvil Cell (DAC) and its attached devices. Using this apparatus, the dissolution processes of calcite (limestone) or dolomite (dolostone) in acidic fluids, including CO2-containing solution, hydrosulphuric acid and acetic acid, under continuously changed temperatures and pressures are simulated. These processes are continuously observed and analyzed under microscope and by Laser Raman Spectroscopy, for which these experiments are called in situ, visual and semiquantitative-quantitative. The Amount of Dissolution (AOD), other than the Velocity of Dissolution (VOD) used by the former researchers, is introduced to represent the dissolution extent of calcite (limestone) or dolomite (dolostone) in different fluids under different temperatures and pressures. The experimental results, combined with the geological analyses on the Sichuan and Tarim basins, are used to indicate the formation mechanism of the dissolution pores in deep buried carbonate reservoirs. In this meaning, this research is attempting to provide theoretical and experimental data for the prediction of carbonate reservoirs.

深部碳酸盐岩储层已成为国内外油气勘探的热点，但其储层溶蚀孔隙形成机理问题一直是争论的焦点，同时也是研究的难点。在前人实验工作的基础上，为了更真实地模拟地下溶蚀过程，以溶蚀热力学理论计算提供溶蚀理论模型、以四川盆地和塔里木盆地典型碳酸盐岩储层为基础建立溶蚀地质模型；引入金刚石压腔及其配套装置作为开展实验研究的主要设备，对不同温度、压力条件下方解石（灰岩）、白云石（白云岩）在不同酸性流体（含CO2水溶液、H2S溶液和乙酸及其混合溶液）中的溶蚀行为进行模拟；实验过程中连续升降温度和/或压力，并利用显微镜和激光拉曼进行原位、可视、（半）定量观测；实验结果利用"溶蚀量"代替前人的"溶蚀速率"来表征方解石（灰岩）/白云石（白云岩）在不同温度、压力和流体环境下的溶蚀差异；最终，结合地质实例分析深部碳酸盐岩储层溶蚀孔隙形成机理，为深部碳酸盐岩储层预测提供理论与实验依据。

深层碳酸盐岩储层溶蚀孔隙形成机理已经成为储层研究的热点和难点。利用自主组装的水热金刚石压腔对封闭体系中不同温压条件下碳酸盐岩与不同酸性流体的溶蚀/沉淀行进行模拟，实现了对实验过程的原位观察和实验结果的原位检测，结合埋藏条件下水-岩平衡体系热力学模拟计算，分析溶蚀孔隙形成机理。结果表明，封闭体系中碳酸盐水-岩体系随着温压升高趋于胶结，但因封闭体系中流体总量少，胶结程度很低，有利于流体占据的孔隙空间被有效保存。气体总量较高的条件下，随着埋深增加溶蚀量先增加后减少；当气体总量较少时，随埋深增加溶蚀量单调减少。考虑深部储层处于相对封闭环境，气体总量较低的情形更接近实际埋藏条件。结合岩石学证据，认为早期孔隙构成了川东北地区深部优质储层的主要储集空间，早期成岩作用控制了优质储层的发育。无论是礁滩型储层还是溶蚀型储层，快速深埋使孔隙迅速被埋藏封闭，水-岩反应处于近封闭的平衡状态，溶蚀-沉淀总体较为有限。总体而言，深部优质储层的孔隙主要来源于沉积期和成岩早期形成孔隙的继承和保存，深埋藏环境主要是储层孔隙保存和调整的场所，孔隙空间的位置可能重新分配。