Key Technologies for Developing Marginal Oil Fields in Offshore China

The majority were marginal oil fields among recent oil fields development projects in China's coastal waters. Because CNOOC's technical breakthroughs in reservoir, drilling and completion, production, and marine engineering, the efficiency of marginal oil field development in offshore China was clearly improved; resulting in a commercial value with huge comprehensive benefits for many marginal oil fields. This paper would use Oilfield ‘A’ in Bohai Bay Basin as an example to describe how a reservoir engineering team improved economics of a marginal oilfield with reserves less than 27 million barrels of oil. First, reservoir engineering research sets the base for efficient development. The reservoir of oil field ‘A’ has the flow channel deposition with only two exploration wells to control nearly 27 million barrels reserves. In order to determine distribution and characteristics of the reservoir, the reservoir engineering team integrated seismic, geological, logging data, well shock calibration of fluvial sand body, detail interpretation of three-dimensional seismic and fine boundary portray, to describe fluvial reservoir sand bodies external morphology and its internal heterogeneity. Based on high-resolution three-dimensional seismic data, the team applied width-extrapolation method from well points and variogram analysis to establish the fluvial reservoir geological knowledge base. By integrating reserve distribution characteristics from analogous oilfield with dense well pattern, the team concluded with three types of well correlation models for fluvial reservoirs: vertical facies changes correlation, stacking sandbodies correlation, and incised channels correlation. The team used above three reservoir characterization techniques to determine the most likely reservoir distribution model of oilfield ‘A’. Base on understanding of the reservoir internal structure, the reservoir engineering team actively explored the application of horizontal well development technology. By using numerical simulation to optimize the length of the horizontal section, the team analyzed vertical distance of well trajectory from the oil-water interface, studied impact of interlayer, evaluated benefit of horizontal injection well, developed practices in horizontal well suitable for channel deposition reservoir. The team utilized this model for designing oilfield development program and achieving maximum oilfield deliverability.