A Successful Project of Progressive Exploration and Development for Shallow Gas Reservoir in Chenjiazhuang Arch

Abstract Aimed at the characteristic that gas-bearing formation of shallow gas reservoir (SGR) shows bright spot on seismic cross-section, integrative technology research combining exploration and development has been developing in Shengli Oil Fields. After several years’ practice, a series of techniques of progressive exploration and development with high benefit for SGR have been created. Studies and practice prove that bright spot on conventional seismic section has nature of multi-solution, i.e. some kinds of reservoirs, such as lithologic reservoir, hydrogenous sandstone, gas bearing hydrogenous sandstone and gas bearing sandstone, all show the characteristic of bright spot. In order to solve this problem, special purpose processing involving 3D, G-log and amplitude versus offset (AVO) is used to distinguish between real bright spots and false ones. Four gas-bearing regions including Yanjia, Chenjiazhuang, Gunan and Sanhecun have been discovered and put into production since 1988. 162 probable bright spots have been found, and 60 new wells drilled with 56 successful wells. Drilling success ratio advances from 55% to 93.3%. Incremental proven gas bearing area is 48.2 km2 with gas initially in place 4.304×109m3, and gas rate is 375×103m3/d. The spread application for this technology has been seeing considerable economic benefit, and it provides practical experience for exploiting such kind of reservoirs also. Progressive exploration and development utilizing technology of seismic bright spot accelerates the step of getting production. Four steps, including special purpose processing and seismic data interpretation, programming development plan and fulfilling drilling and gas lines construction, gaining gas productivity and submitting proven reserves, are all accomplished in the same year. This paper introduces a typical example for the course of progressive exploration and development in Chenjiazhuang Arch. Introduction Seismic recognition technique for gas reservoir may be used to study reservoir lithology and petrophysical properties, oil-gas-water distribution areally and spatially and structural configuration, to predict hydrocarbon abundance zones, and to provide basis for decision making of gas field reserves calculation and development plan designing.1 Thus the quantity of appraisal wells can be reduced. It is an important technical way to realize more output by few investment.2 But its application was principally limited in hydrocarbon exploration stage. Reservoir cementation of shallow gas reservoir (SGR, less than 1,500 meters usually) is very unconsolidated in Jiyang Depression. And its density would reduce as sandstone filled with gas, thus propagation velocity of seismic compressional wave would decline rapidly. That results in the fact that wave impedance of gas bearing formation is much less than that of shaly host rock. Higher reflection coefficient comes into being at both top and bottom surfaces of gas bearing formation, and thus shows abnormal reflected wave of strong amplitude on seismic record cross-section, i.e. bright spot. This is the fundamental principle of SGR exploration utilizing seismic bright spot.3