Abstract
Tight gas is an important unconventional resource with continuous consumption demand, and co-production from multi-layers are becoming an inevitable choice for areas with low reserve abundance. The Ordos basin contain tight gas production from generally the whole Permian, recording sandstones deposited from transitional to terrestrial environments. In order to reveal the reservoir sensitivities of different layers, petrophysical and sensitivity experiments were conducted with samples from members of different sedimentary environment, i.e., Tai 2 Member (Pit2, coastal environment), Shan 1 Member (PiSi, deltaic environment), He 8 Member (P2X8, deltaic-fluvial environment), He 4 Member (P2S4, fluvial environment), and Qian 5 Member (P3S5, braided fluvial environment) of Permian. The results showed;; (1) The sandstones of P1t2, P1S1, P2X8, P2S4, and P3S5 are dominated by feldspathic litharenite, litharenite, lithic arkose, litharenite, and lithic arkose, respectively;; (2) From P1t2 to P3S5, the content of illite decreases, those of chlorite and illite/smectite (I/S) increase, and kaolinite firstly increases and then decreases (the trend changed in P2S4);; (3) The permeability of all the analyzed sandstones ranges between 0.2 and 0.6 mD, the average porosity between 5.7% and 8.2%, with mercury withdrawal efficiency between 32.8% and 42.1% and average median radius between 0.10 and 0.20 μm; (4) All the sandstones have medium-weak flow rate sensitivities, with medium-weak (P1t2), medium (P1S1), medium (P2X8), medium (P2S4), and medium-weak (P3S5) water sensitivities and weak (P1t2), medium-weak (P1S1), medium-weak (P2Xg), medium-weak (P2S4), and medium (P3S5) alkali sensitivities. The flow rate sensitivities are mainly influenced by pore structure and the quartz content, while water sensitivities are affected by pore structure, I/S and illite contents, and the alkali sensitivities are correlated with pore structure and kaolinite, I/S, and feldspar contents. The results can be beneficial for tight gas production engineering choices and strategies for improving gas production.
NSTL