| Reef-bank of Sichuan Basin have been explored along the platform margin belt on both sides ofthe Kaijiang-Liangping trough for a long time. Correspondingly, a series of major breakthroughs havebeen obtained and a number of large oil and gas fields have been found. After the breakthroughs ofKaijiang-Liangping trough, how reef-bank exploration will proceed? Is there another“Kaijiang-Liangping trough” in Sichuan Basin? To find another "Kaijiang-Liangping trough", muchresearch have been performed and Yanting-Tongnan trough has been discovered in Central SichuanBasin in our study. The following conclusions have been accomplished in this paper:（1）Sichuan Basin underwent intracratonic rift and basement fault activities in Late Permian,developing a paleogeography framework of " three uplifts and three depressions" under the backgroundof the regional large ramp, including Exi-Chengkou trough, Kaijiang-Liangping trough andYanting-Tongnan trough. Reefs were usually developed surrounding the platform margin, gathered asgroups and spread as strips.（2）Based on sedimentology and tectonics dynamics analysis, data of drillings, outcrops andseismic, Yanting-Tongnan trough has been discovered in Central Sichuan Basin. Similar toKaijiang-Liangping trough, another platform margin reef belt distributes along a U-shape belt aroundYanting-Tongnan trough, which is expected to become another natural gas accumulation zone after theplatform margin around Kaijiang-Liangping trough. But compared to Kaijiang-Liangping trough,Yanting-Tongnan trough is relatively shallower and smaller, and the scale and quality of reef-bankreservoirs in its margin belt is a little poor relatively（3）34reef-banks have been predicted on the platform margin of Yanting-Tongnan trough by theintegrated study of seismic facies and seismic attribute analysis and the area of reef-banks is over5714km2. Reed-banks can be divided into two stages, the first of which is wide distribution and large area andthe second is fewer distribution and smaller area. Reef-banks from first stages to second stages migratefrom platform margin to trough gradually.（4）As for Yanting-Tongnan trough, the platform margin reef-bank bodies were mainly developedin the upper Changxing formation. In the western Moxi-Zhongjiang region it is mainly bioclasticlimestone and in the eastern Guang’an-Gongshanmiao region is dominated by dolomite. Based onidentification under microscops and geochemical analysis, burial dolomitization and karstification controlthe formation of effective reservoir and the sea water of Changxing period is the dolomitizing fluids.（5）Based on identification under microscops and geochemical analysis, argillaceous rock in theYanting-Tongnan trough is effective source rock, TOC of which is0.65-1.87%and Ro is1.30and thetype of organic matter is Ⅰ-Ⅱ1. This source rock is important supplement for major source rock.（6）Two favorable exploration regions are proposed in the Yanting-Tongnan platfrom margin bycomprehensive analysis of exploration achievements and seismic prediction result. One of which isGuang’an-Gongshanmiao region whose area is4860km2and13reefs have been pridicted. And anotheris Moxi-Zhongjiang region, whose area is4600km2and21banks have been pridicted（7）The discovery of Yanting-Tongnan Trough significantly improves the former understandingthat Kaijiang-Liangping trough is controlled by the development of reef-bank bodies. It changes thesingle deposition facies model in Central Sichuan. This discovery expands the favorable reef-bankexploration areas from the south to Central Sichuan. The favorable reef-bank exploration area increasesfrom original2×104km2on both sides of Kaijiang-Liangping trough to more than5×104km2inYanting-Tongnan trough platform margin belt and Kaijiang-Liangping platform margin belt. Thereef-bank exploration range is significantly expanded. |
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