Controls On The Complicated Reservoirs And Prediction Of Effective Sandstone Distributionin Sulige Gasfield

The He8 gas pool in Sulige gas field is a kind of wide spreaded lithologic gas pool with low pressure, low permeability and low reserve abundance. The effective sandstones are those relative high permeable units distributed among the low permeability background. Because of their deep buried depth, little size and thin thickness, prediction of effective sandstones proves a tough task for gas field development. Integrated studies were carried on in such aspects as sedimentary microfacies, diagenesis, log interpretation, relationship of lithofacies-petrophysics-log response-gas saturation, close well drilling and the seismic response of gas sandstones. Then deep understandings of the genesis and distribution of effective sandstones were gained. A new prediction method for effective sandstone distribution was put forwards, and favorable areas were predicted. The main achievements of this dissertation are followings: 1. Only the coarse grained and conglomeratic sandstones in the braided channel sandy sediments can be effective sandstones, while the medium and fine grained sands would be invalid. The coarse grained sands are mostly distributed in the channel bars and the bottom of some channel filling sediments. The medium and fine grained sands are mostly distributed in the channel filling sediments. Two kinds of channels-high energy channel and low energy channel-were identified in the braided multi-channel system in the He8 intervals. The high energy channels control the distribution of main channel bars. 2. The study of the genesis of effective sandstones illustrates that there is a close connection among sandstone grain size, sandstone ingredients and their petrophysics. Because of the depositional separation of different clast, the coarse sandstones are inclined to be relative high reservoir quality, with high content of hard quartzite clast and quartz grains, which favors the preservation of primary pores, the flowing of pore flows and occurrence of secondary pores. The medium and fine grained sandstones are inclined to be bad or invalid reservoir quality, with high content of soft lithic fragments, which leads to tight compaction, poor preservation of primary pores and poor development of secondary pores. So, it can be put forwards that depositional hydro-dynamics controls the sandstone structure and component, and then controls the diagenesis and pore evolution. Based on the relationship of sedimentary microfacies, lithofacies, diagenetic facies and petrophysics, the genetic and distributed models of the four kinds of sandstones in the He8 intervals were built up. 3. The sandstones in Sulige gas field are wide spreaded, while the effective sandbodies are dispersively distributed with small size and poor continuousness and connectivity. The width of a single effective sandbody is almost less than 800 meter. The effective sandbodies are distributed in the tight sandstones and mudstones in shapes of isolated points or narrow strips. 4. Suffering from the deep buried depth, thin thickness and the limit of seismic resolution, the prediction of gas sandbody distribution is difficult. Through establishing geological models of different kinds of gas wells, and integrated studying of the geological models and their AVO response on the 2D lines, the favorable areas were picked up for recent development.