Hydrocarbon accumulation conditions and key exploration and development technologies for PL 19–3 oilfield

The PL 19–3 Oilfield is the only super-large monolithic oilfield with oil and gas reserves up to 1 × 109 t in the Bohai Bay Basin, and it has been successfully developed. Exploration and development practices have provided abundant data for analyzing formation conditions of this super-large oilfield. On the basis of the exploration and development history, fundamental reservoir features, and with available geological, geophysical and test data, the hydrocarbon accumulation conditions and key exploration & development technologies of the PL 19–3 Oilfield were discussed. The key conditions for forming the super-large Neogene oilfield include four aspects. Firstly, the oilfield is located at the high position of the uplift that contacts the brachy-axis of the multi-ridge slope in the biggest hydrocarbon-rich sag in the Bohai Bay Basin, thus it has sufficient hydrocarbon source and extremely superior hydrocarbon migration condition. Secondly, the large-scale torsional anticlines which formed in the Neogene under the control of the Tanlu strike-slipping movement provide sufficient storage spaces for oil and gas preservation. Thirdly, the “multiple sets of composite reservoir-caprock assemblages” developing in the special shallow-water delta further contributes greatly to the effective storage space for oil and gas preservation. Fourthly, due to the coupling of the uplift and strike slip in the neotectonic period, extensive faulting activities constantly released the pressure while the late period massive hydrocarbon expulsion of the Bozhong took place at the same time, which assures the constant and intense charging of oil and gas. The super-large PL 19–3 Oilfield was controlled by the coupling effects of all those special geologic factors. In view of this oilfield's features (e.g. violently reformation caused by strike slip, and the special sedimentary environment of shallow-water delta), some key practical technologies for exploration and development have been developed. Such technologies include: the special prestack depth migration processing for gas cloud zones, the prediction of thin interbed reservoirs based on high-precision inversion of geologic model, the reservoir description for the shallow-water braided river delta, the quantitative description for remaining oil in the commingled oil reservoirs with wide well spacing and long well interval, and the well pattern adjustment for formations during high water cut period in the complex fluvial-facies oilfields.