塔中地区深层低丰度碳酸盐岩有效烃源岩评价 及其对油气藏贡献
Evaluation of Deep Carbonate Source Rocks with Low TOC and Contribution to Oil-Gas Accumulation in Tazhong Area, Tarim Basin

热演化程度较高、有机质丰度偏低的碳酸盐岩烃源岩的有效性及其对油气藏的贡献评价正成为影响我国深层碳酸盐岩油气勘探的一个关键性问题.以塔中地区为例，通过有效烃源岩TOC下限确定、有机质丰度的测井响应和影响因素分析，建立了碳酸盐岩烃源岩判别标准，研究了低丰度(TOC≤0.5%)烃源岩的地化和地质特征，利用物质平衡数值模拟法和生烃潜力法评价了低丰度烃源岩对油气藏的相对贡献.结果表明：未成熟、成熟、高成熟和过成熟阶段的碳酸盐岩有效烃源岩TOC下限分别是0.50%、0.30%、0.20%和0.15%；碳酸盐岩烃源岩测井响应与泥质烃源岩的测井响应有相同点也有差异，其中自然伽玛、声波时差和弹性参数响应特征相同且与TOC关系较好；烃源岩有机质丰度主要受沉积环境、岩石颜色、岩性的影响.低丰度烃源岩的厚度为24～500m，占地层总厚度的37%左右，是高丰度烃源岩厚度的1.54～5.92倍.根据排烃量、有效排烃量、可供聚集烃量和可供资源量评价，低丰度烃源岩对油气藏的相对贡献分别为32.6%、27.4%、30.7%和29.6%，在理论研究和资源评价中不可忽略.
As oil and gas exploration is conducted in deep and super-deep layers, effectiveness and contribution to oil-gas accumulation of carbonate rocks with high thermal evolution and low organic matter abundance (TOC≤0.5%) in deep layer need to be reevaluated. This is a key scientific issue for oil and gas exploration in carbonate rocks in China. Taking Tazhong area as an example, a qualitative discriminating criterion for carbonate source rocks was established by determining the lower limit of TOC, analyzing logging response and influencing factors of organic matter abundance. Geochemical and geological characteristics of carbonate source rocks with low TOC (CSRLTOC) in Tazhong area were studied, and their contribution to oil-gas accumulation was evaluated by numerical simulation and hydrocarbon generation potential. Results show that the lower limit of TOC for effective carbonate source rocks with immature, mature, high mature and over mature stages are TOC=0.50%, TOC=0.30%, TOC=0.20% and TOC=0.15%, respectively. The log responses of carbonate source rocks have some differences from those for mudstone. The relationship of TOC, natural gamma, acoustic slowness and elastic parameter are better. The organic matter abundance is influenced by sedimentary environment, color of rock, and lithology. Based on above results, the discriminating criterion was established. In the Tazhong area, the CSRLTOC is less than none source rocks, with 24-500m, accounting for 37% of the total thickness. The thickness of CSRLTOC is 1.54 to 5.92 times of those source rocks with high TOC (TOC＞5%).On the basis of the amounts of hydrocarbon expulsion, the amounts of effective hydrocarbon expulsion, the amounts of hydrocarbon accumulation and the amounts of oil-gas resources, the contributions of the CSRLTOC to oil-gas accumulation are 32.6%, 27.4%, 30.7% and 29.6%, respectively. Therefore, CSRLTOC should not be neglected in the theoretical research and resource evaluation