With well development of rift and karst

carbonate rock stratum might be a high quality of reservoir

Tahe No.4 oilfield is a typical example.The rift can be divided into various types on the basis of factors of its distribution pattern

occurrence

size

filling

connection and origin.stages division of the rift can be done according to various intersect relations of the rift

various filling compositions

filling stages

logging corresponding characteristics and different structural stress fields.Lithology

rock stratum thickness

fracture process

structural stress field

local structure

stratum load and karst process are all main controlling factors for the development of the rift.Palaeokarst process mainly consists of several types of sediment karst

weathered crust karst and karst of rift-cavity system etc.Paleaokarst had experienced periods of syndeposition

crust of weathering

burial and epigenetic variation in the course of evolution.Paleaokarst might be classified

paternally as karst trace

karst cave

karst pore and cave

vertically as surface karst belt

seepage flow karst belt and underflow karst belt.The development of paleaokast is controlled by several factors of climate

lithology

structure

hydrology and landform.The study of karst of rift-cavity system shall be divided into 3 stages:study karst of rift-cavity' occurrence

organizational system

development

origin

filling and distribution by observing outcrops and rock cores.Distinguish regularity of rifts and their distribution and development by studying and interpreting data collected from well drilling

logging

seism and rifts logging etc.predicate karst of rift-cavity by seism

logging and simulation of structural stress fields.The study of karst of rift-cavity system shall be based on improving and perfecting available technical methods

enforcing application of new technical methods

stressing the importance and orientation of comprehensive application of various methods by seeking more effective theories and technical methods.