Abstract:

To study burial diagenesis is very important for reservoir assesment.Petrological datafrom 66 wells suggest that the present temperature corresponding to the depth where burial diagenetic minerals occur is approximate or equal to the formation temperature.There-fore,the original formation temperature of the burial diagenetic minerals can be calculated by following equation.T=G(H-h)+14.5℃ where T is the original formation temperature of the burial diaganetic minerals;G isgeothermal gradient;H is the shallowest depth where this diagenesis occurs;h is the depth of constant temperature zone(assuming h=0 when T is calculated because it is very small in study area);14.5 is the annual average surface temperature in the area.Calcula-tion and error analysis show that the original formation temperature of different burial dia-genetic geother mometer are as follows.65±5℃ for weak over growth of quartz;90±5℃ for intensive over growth of quartz;92±5℃ for authigenic garnet;95±5℃ for late car-bonate cement(such as saddle dolomite);70±5℃ for authigenic kaolinite;140±10℃ for trans formation from kaolinite to illite.Based on all the diagenesis related to tempera-ture,four diagenetic zones can be divided,i.e.shallow,moderate,deep and superdeep zones.It is demonstrated that these zones can be used to classify and assess reservoir rocksand source rocks.