Deep Hydrothermal Altered Dolomite Reservoir in the Tarim Basin Northwestern China

TS1 well in the Tarim basin reveals that high quality reservoir of deep Cambrian dolomite (deeper than 8000m) develops porosity as high as 9.1%, and shows increasing trend in porosity with increasing depth. Dolomite filling in vugs or fractures in the Cambrian dolomite matrix shows curved crystal surface and undulose extinction. Compared with matrix dolomite, the filling dolomite has relatively high Fe, Mn and Ba contents. In isotope compositions, the filling dolomite is relatively light in oxygen isotope but has relatively high 87Sr/86Sr values. The above characteristics indicate that the infillings of the dolomite and other minerals are related to activities of deep hydrothermal fluids which were related to the strong Permian magma activity. Based on petrology, mineralogy, and geochemistry analysis of cores, and combined with geophysics features, deep dolomite reservoir has first gone through meteoric water dissolution during contemporaneous / penecontemporaneous stage, and then been altered and dissolved by deep hydrothermal fluid during deep burial stage. This research indicates that deep and ultra-deep carbonates still possess good exploration prospect under the influence of deep hydrothermal fluid, which is significant to the deep oil and gas exploration worldwide.