塔中与塔河地区奥陶系岩溶储层形成条件的差异

对比研究表明,塔中、塔河地区奥陶系岩溶型储层存在显著差异,塔中奥陶系白云岩储层以小型岩溶孔洞为特征,而灰岩储层以发育局限的岩溶洞穴型储层为特征;塔河地区岩溶洞穴型储层以大面积、多层系、叠置连片的分布为特征。造成塔中、塔河地区奥陶系岩溶型储层差异的主要原因是构造演化、古地理岩相和可溶岩岩石类型之间的差异。加里东中期塔中地区冲断褶皱强烈发育,可溶的白云岩或灰岩地层呈窄条带状分散出露,岩溶斜坡发育局限;塔河地区构造活动微弱。海西早期塔河地区整体抬升幅度大,地层强烈剥蚀夷平,可溶的灰岩地层大面积平缓出露,岩溶斜坡发育,大气水沿先前的裂隙系统流动并呈管状流溶蚀改造裂隙,形成大型洞穴系统,多套洞穴储层大面积多层系叠置连片分布;塔中地区构造活动却相对平缓。因此,塔中地区以加里东期岩溶为主,塔河地区以海西期岩溶为主。

Differences between formation conditions of Ordovician karstic reservoirs in Tazhong and Tahe areas

Comparative study shows that Ordovician karstic reservoirs in Tazhong and Tahe are quite different. In Tazhong, Ordovician dolomite reservoirs are characterized by small karst vugs, and limestone reservoirs are characterized by limited karst caves. While the karst cavernous reservoirs in Tahe are characterized by superimposition of multiple series of strata and continuous distribution in a large area. The main factors that have caused the differences of Ordovician karstic reservoirs in Tazhong and Tahe are tectonic evolution, lithofacies palaeogeography and dissoluble rock types. In Middle Caledonian, thrusting and folding were strong and well developed, dissoluble dolomites or limestones were dispersedly outcropped in narrow strips, and karst slopes were developed limitedly in Tazhong area; while tectonic movement in Tahe area was weak at that time. In Early Hercynian, Tahe area was wholly and largely uplifted, resulting in formations being strongly denuded and leveled, dissoluble limestone strata being flatly outcropped in large area, and karst slopes being well developed. Meteoric water flowed along the existing fracture systems and dissolved and reconstructed them in tubular flow, resulting in large cave systems. Several sets of cavernous reservoirs are distributed in large areas, due to multiple series of strata being superimposed and interconnected. However, tectonic movement in Tazhong was relatively moderate in Early Hercynian. Therefore, Tazhong area was dominated by Caledonian karst, while Tahe area was dominated by Hercynian karst.