Fine Description On Terrestrial Low-permibility Reservoir

There are huge oil and gas resources in terrestrial low-permeability reservoir in China.It is a great challenge to reservoir geologists on how to enhance oil recovery and oil production rate in such tenestrial low-permeability reservoir.The author takes the meandering river and delta and lake reservoir in Chang-1 and Chang-3 Formation of YanChang Group of Triassic in H152 Block of Huachi oilfield as example. Stratigraphy sequence,sedimentary and geology are applied to build original geology model through the study of target reservoir's stratigraphy,microfacies,lithology and heterogeneity.The Petrel software is applied to build the porosity,permeability and saturation 3D model based on stochastic technology.Laboratory results are used to study the sensitivity character of reservoir.These scientific studies provide geology realization for the reasonable development of low-permeability reservoir and resource.This study combines the sequence stratigraphy and stochastic modeling and reservoir protection together,consummating reservoir description technology of low-permeability reservoir,it can be applied to similar geological reservoir.The main conclusions and creative ideas are as follows:①Applying Vail's classical sequence stratigraphy principles and manners,based on synthetic study of core,drilling and logging data, upper Triassic Chang-1 and Chang-3 Formation in H152 Block are divided into three third-order sequences.There are two third-order sequences which consist of transgressive and highstand system tracts in Chang-3 Formation,forming classical stratigraphy pattern in depression lake basin.Lowstand system tract is developed in Chang-1 Formation which forms terrestrial flood stratigraphy with type-Ⅰsequence boundary.②The Chang-1 and Chang-3 oil reservoir belong to meandering river—meandering river delta—lake sediment.The Chang-1 has the characteristic of binary structure of meander river sediment,the reservoir sandstones are developed in lowstand system tract.The graded coarsening-upward reverse cycles in Chang-3 reveal its characteristic of river-controlled delta,and the reservoir sandstones are developed in highstand system tract.The sedimentary development and distribution have been discussed within the sequences.The underwater distributary channel and river mouth bar sediments are pointed to be the main reservoir sandstones in the principal producing formation.③The type of rock are arkoses and lithic arkoses,their main pore type is intergranular dissolved pore,medium pore—fine throat and small pore—minisized throat are their primary pore—throat structures.The reservoir sandstones are found to be in the A-substage of middle diagenesis,and the reservoir has the characteristic of low-permeability which has interlayer,intrastratal and plane heterogeneity.④Protogeological model has been built based on overall studies which fully took advantages on the vast data set comprising log,core, production tests,laboratory data,and on better understanding of the heterogeneity nature supported by high intensity of drainage points. Petrel software package is employed to visualize the 3D volume of the reservoir and spatial distribution of properties based on geo-statistical and stochastic modeling techniques.⑤The sensitive mineral types and their damage mechanisms have been analysed systemically.The experiments show a variety of sensitivities of the target formations to high flow rate fluid and injected water incompatible with the formation water:weak water sensitivity, weak—medium rate sensitivity,general no acidic sensitivity with exceptions,weak—medium alkaline sensitivity,and weak salt sensitivity. Scale tests showed that calcium carbonate and calcium sulfate may be arised from the reaction between incompatible injected water and the formation water.This research is of advantage to reservoir protection.