Fault-caprock Matching Relationship And Its Controlling Effect On Gas Accumulation And Distribution

In order to study fault-caprock matching relationship and its controlling effect on gas accumulation and distribution in Nanpu Sag,based on using geological datas of geochemistry,drilling,logging,oil-gas testing and three-dimensional seismic,in combination with the geological background of Nanpu Sag,fully understand the regional structure and evolution characteristics,formation development and sedimentary characteristic as well as source-reservior-caprock type and characteristics in the study area,caprock and gas-source fault as the main study object,quantitative study fault-caprock matching relationship and its controlling effect on gas accumulation and distribution in Nanpu Sag.First of all,in the typical single wells containing gas cover caprock horizon,using the method of combination of wells and seismic,linking wells profile as the skeleton,tracking the top and bottom reflective interface of caprock in the seismic,single well columnar as a basepoint, linking wells profile as a baseline to expand,tracking the development and distribution of caprock in the Landmark,to get the distribution characteristics of the caprock;Secondly,on the basis of the study geometry characteristics and kinematic characteristics of fault,using the method of fault growth index,section stretching rate and tectonic evolution section to determine the activity times of fault,analysis of the formation and evolution history of fault,and then divided into four sets of fault systems:early closing fault((1) type),late transporting fault((2) type),middle-late transporting fault((3) type) and early-middle-late transporting fault((4) type),combined gas accumulation critical period,to determine gas-source fault.Based on this,analysis of theoretical basis of fault-caprock matching relationship seal gas,the study found:theoretical basis of fault-caprock matching relationship sealling gas is that the upper and lower of gas-source fault is not connected distribution in regional caprock,the main influencing factors are caprock thickness and fault throw.Refer to the parameter of “faulted thickness of caprock” to quantitative expression the ability of fault-caprock matching relationship sealing gas,summed up the study method of forecasting fault-caprock matching relationship sealing gas area,and apply it to the study area.The results show:(1)When faulted thickness of caprock is bigger than the upper and lower of gas-source fault un connected distribution required minimum faulted thickness of caprock,fault-caprock matching relationship can seal gas,gas can only accumulation and distribution in the reservoir under the caprock;(2)When faulted thickness of caprock is smaller than the upper and lower of gas-source fault un connected distribution required minimum faulted thickness of caprock, fault-caprock matching relationship can not seal gas,gas can accumulation and distribution in the reservoir over and under the caprock.Tn the end,summed up fault-caprock matching relationship and its controlling effect on gas accumulation and distribution in the study area have the following four kinds of accumulation modes:(1) the bottom sealing gas of fault-caprock matching relationship accumulation mode;(2) the middle sealing gas of fault-caprock matching relationship accumulation mode;(3) the top sealing gas of fault-caprock matching relationship accumulation mode;(4) bottom- middle-top all not sealing gas of fault-caprock matching relationship accumulation mode.