Appraise Method And Application Of Fault Lateral Seal Ability

On the basis of the investigation of a large number of domestic and foreign literatures, it is considered that lateral seal mechanism of fault is that there is differential permeability between fault zone and surrounding rock. Based on the geologic process of differential permeating caused by fault activity, fault seal type can be divided into juxtaposition seal and fault rock seal. The type of fault rock seal can be divided into: disaggregation zone, cataclastic rock, phyllosilicate-framework fault rock, clay smear and cemented fracture. The geological processes of fault rocks forming lateral seal include disaggregation mixing, diffusive mass transfer, cataclasis, cementation and clay smearing. Lateral seal ability of fault with the type of lithology juxtaposition seal can be evaluated by use of Allan and Knipe graph. For fault with the type of fault rock seal, we can simulate the material composition in fault zone by calculating fault zone seal attribute value SGR, and then establish the relation between SGR and oil column height which sealed by it, namely lateral seal-failure envelope of fault. The lateral seepage place of fault depends on three-dimension distribution of lateral seal ability of each point in fault zone which established by using SGR. By statistics on fault throw changes along strike of Xuzhong controlling-depression fault in Xujiaweizi, and combining with Knipe graphs of wells around Xuzhong fault, fine dissection on gas reservoirs controlled by Xuzhong fault is conducted. The results shows that if volcanic rock reservoir juxtaposes non-volcanic rock by fault, volcanic rock reservoir is rich in gas and fault seal ability is strong; if volcanic rock juxtaposes volcanic rock by fault, volcanic rock is generally water-cut or dry layer and lateral seal ability of fault is very weak. Fault throw mode of strike-slip fault of Xuzhong fault makes gas reservoirs on both sided of it present the distribution mode of"one increase with the other decrease". By establishing function relation between SGR value of fault zone and oil column height which sealed by fault in the lateral side, later seal ability of fault in Beier depression is studied quantitatively. The results show that SGR value of fault zone has exponential relation with oil column height which sealed by it, and fault lateral seal ability depends on 3-dimension distribution of SGR value of fault plane. By using the function formula of lateral seal-failure envelopes of faults established by data of reservoir in Bei 301 block, it is predicted that OWC of Huhe 16 trap is -1025m, which has been confirmed by drilling. Generally, the lateral seal ability of faults in Beier depression shows that seal ability above Nantun formation is stronger vertically and that in the southwest of Beier depression is the stronger in the plane, which provides the reference for further exploration of traps in this area.