Burial Diagenetic Geothermometer and the Classifying Characteristics of the Burial Diagenetic Zones of Tertiary Clastic Rocks in Shengli Oil Field, East China

Abstract

It is very important to study burial diagenesis for reservoir assessment. During the Cenozoic Era, the studied area was a downfaulted depression basin with continuous subsidence that was filled by thick clastic sediments. Based on the petrological data from 66 wells in this basin, the present geotemperature corresponding to the occurring depth of the burial diagenetic event approximates or is equal to the initial temperature of the diagenetic event. Therefore, the initial temperature of the burial diagenetic event can be calculated by this equation: T = G(H {minus} h) + 14.5C, where T is the initial temperature of the burial diagenetic even; G is geothermal gradient; H is the shallowest depth for this diagenesis occurrence; and h is the depth of constant temperature zone. The annual average surface temperature of the studied area is 14.5C. The different burial diagenetic geothermometers calculated by the equation are as follows: 65 {plus minus} 5C for minor quartz overgrowth; 90 {plus minus} 5C for intensive quartz overgrowth; 75 {plus minus} 5C for epidote dissolution; 92 {plus minus} 5C for authigenic garnet; 95 {plus minus} 5C for late carbonate cement; 140 {plus minus} 10C for transformation from kaolinite to illite. Based on all the burialmore » diagenetic geothermometers, the burial diagenetic sequence can be divided into shallow ( 130C) zones. It is demonstrated that these zones can be used to classify and assess the reservoir rocks and source rocks.« less