The Study of Clay Minerals Distribution in Lianhua Reservoir

Key words: 
• Lianhua reservoir /
• clay minerals /
• steam flooding /
• sedimentary facies reservoir /

Abstract: The Lianhua reservoir of Shahejie group( geology period E1)in Gaosheng Oil field located in Liaohe granen faulting hasi, is rich in heavy crude oil, with the burial depth being 1 450-1 700 m. The reservoirs have been under development for 22 years.The company has made great profit from the reservoir development by means of steam-flooding technology but some problems have been found in the reservoir with the technology application, because the difficulty in reservoir development is increasing with the frequency of applying the technology.Bv the end of 1998 the average steam flooding for every well has been four times but the more steam-flooding the less satisfactory the efforts to increase the production. Therefore a more comprehensive study of the types content and the horizontal and vertical distribution characteristics of the clay minerals in the reservoir is of most important consequence to the design of the heavy crude oil development reservoir protection reservoir evaluation and enhanced oil recovery(EOR) etc.The clay minerals in Lianhua reservoir are systematically studied by means of X-ray diffraction scan electronic microscope and heat simulation experiments. The Lianhua reservoir is a sediment by gravity flow, with the rock types being gravel, sandstone, and mudstone, and the sedimentary depth being 50-600 m.Lianhua reservoir has excellent physical property, with the porosity being 20 %-26 % and the permeability being 1-4μm². The studies show that the major clay minerals in Lianhua reservoir are montmorillonite( 60%-85%),illite(8 %-20 %),kaolinite(5%-25%),and chlorite(<5%).The montmorillonite content decreases with the increase of the burial depth but the kaolinite and illite content are just the opposite because the porosity fluid in sandstone and gravels more easily circulative than that in mudstone, and the montmorillonite in sandstone can more easily convert into other claw. For the study of the relationship between oil saturation and clay types the rock is divided into two groups according to the oil saturation degree: the oil-saturated and non-saturated.The statistical result shows that the clay minerals content and clay types have nothing to do with the oil saturation percentage. The types contents and distributions of clay minerals are mainly controlled by rock types and sedimentary fades.In general the absolute content of the montmorillonite increases with decrease of the sedimentary rock grains.The montmorillonite in gravel and sandstone has a relatively lower content than that in mudstone, but there is no much difference between the gravel and sandstone in their contents of montmorillonite.The relative content of montmorillonite in gravel and sandstone is 53.88%-85.99 %,with an average of 67.94 %,while the content in mudstone is 69.54%-86.59 %,with an aver- age of 79.02 %.The relative contents of kaolinite distribution decrease in the sequence of gravel sandstone and mudstone. But that of the illitc is just the opposite.Lianhua reservoir is a turhiditv current deposit in lake facics.Sandstone and gravel are mainly distributed in groove and branch groove facics, mudstonc and alcurolitc in deep lake,groove front margin and intcrlavcr branch groove facics.During the evolving process of the facics from the main groove to branch groove to the groove front margin, to the intcrlavcr branch groove, and finally to deep lake, the absolute content of clay minerals and the relative content of montmorillonitc in Lianhua reservoir increases with the decline of the primary hydraulics. Bv heat simulation experiments and a comparative study of the distribution characteristics of clay minerals before and after the steam flooding,it is found that the montmorillonitc in the reservoir can increase because of kaolinitc's reaction to carbonate grains.But because the heavy crude oil carries the montmorillonitc grains out, there finally is an approximately 1%deduction of the absolute amount of montmorillonitc in the reservoir after steam flooding.Because the steam flooding can destroy the clay microstructure to a large degree, some clay minerals disperse and migrate to increase the microheterogeneity parameters of reservoir. According to the types, contents and distributions of the sensitive minerals, the main mechanism of formation damage during steam flooding is particle migration and swelling of montmorillonitc.Steam has a strong effect to the microstructure of the clay minerals.