Abstract:

The Yingcheng Formation and the Shahezi Formation in the Shiwu oilfield harbor oil/gas reservoirs of low to ultralow permeability in complex faultblocks. Single thin sand bodies there distribute unevenly and are compartmentalized by faults in certain places. Fluids of various types inside the reservoirs are controlled both by structure and lithology. Most wells drilled in the field have to be fractured before production with only a few can produce by natural energy. Performance of production test in single wells shows a low formation volume factor, a bigger startup pressure gradient (meaning a low production), and a faster production declining rate for wells in natural depletion. The results also suggest that wells producing both oil and gas have a better performance than those produce oil only, and gas wells are the most productive ones. To tackle these problems, we proposed a comprehensive development strategy which includes the following aspects. The first is performing a separatelayer fine reservoir description based on separatelayer fracturing, testing and evaluating. The second is increasing single well production capacity by commingled production after separatelayer fracturing and supplementing formation energy with wholelayer water injection followed by separatelayer water injection. The third is carrying out water injection pilot with irregular well patterns in the selected favorable fault blocks at first and then implementing the successful experience to other areas. The fourth is performing largescale fracturing in gas/oilbearing layers and CO2 huff-n’puff in single oil well with low gasoil ratio.