Faults in Carbonate and their Controls on the Distribution of Karst Reservoir — A Case Study of Halahatang Field in Tarim Basin, China

Liu, Lei; Zhang, Lei; Zhang, Guangya

Halahatang field locates at the southern slope of the southward dip North Tarim paleo-uplift, Tarim basin. Its reservoir is middle Ordovician carbonatite of Yijianfang formation. However, the current burial depth of Ordovician is over 6000 meters, and Halahatang area was used to be thought as a depressed area for a long time, which undoubtedly influenced its petroleum exploration. However, since the success of H7 well in 2009, a number of exploration wells in this area target at Ordovician carbonate karst reservoirs had gotten high industrial production of crude oil. Proved oil has exceeded 792 MMBO, and production of 2012 is estimated 4.4 MMBO.

According to the latest interpretation of 3-D seismic data, we separate all the faults developed in this area into three groups, which are middle-late Caledonian, Hercynian and late Yanshan - Himalayan faults, respectively. To support this view, we also got evidences from fault strikes, incision relationships between different faults and late Ordovician palaeochannels developed in this area. More importantly, our research found that middle-late Caledonian stage of fault is the main controlling factor of karst reservoir.

Middle-late Caledonian faults' NNW-NNE adjoint strike clearly indicates that they were formed by south-north compressional force. Due to their wide distribution and favorable development time, they are most likely to dominate the generation and distribution of karst reservoir. According to seismic section analyses, we found that typical ball chain reflections which represent the existence of karst reservoir are mostly near this group of faults. Maps of seismic amplitude variation ratio could effectively identify the existence of karst caves. Using this technology, we found that ball chain reflections in the middle and south part of research area are mostly developed in the vicinity of middle-late Caledonian faults, while in the north area where used to be uplifted higher, ball chain reflections are distributed extensively. These phenomenons all support that middle-late Caledonian faults dominate the distribution of karst reservoir in this area.

All these faults could act as good hydrocarbon migration pathways. In some part of research area, the late Yanshan - Himalayan faults interconnect the middle-late Caledonian faults, so oil and gas could migrate upward through these faults that could explain the oil and gas indications in some wells within Mesozoic and Cenozoic strata.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013