MARGINAL LACUSTRINE LIMESTONE DEPOSITION AND IMPLICATIONS FOR RESERVOIR DEVELOPMENT, YI64 BLOCK, BOHAI BAY BASIN, P. R. CHINA

John S. Sneider¹, Andrew S. Harper², and Cliff Geng^2
1 Sneider Exploration Inc
² MI Energy Corp

In 2001, operator MI Energy and partner Sinopec drilled Well Y64-1 just 225m west of discovery Well Yi64. Drilled in 1974, Well Y64 had 14+m pay in marginal lacustrine limestone reservoir of the Eocene Shahejie Fm, Member IV (ES4) and IP 2445BOPD. Unfortunately, the Yi64-1 offset well was unsuccessful. Although shows and 2m of log pay were encountered, the ES4 reservoir facies is not developed at the Yi64-1 location, and the well is non-productive.

Studies were undertaken to improve the understanding of the marginal lacustrine ES4 reservoir facies in the Yi 64 Block. A key data item was ES4 core collected in Well Yi64-1. The core was analyzed in conjunction with core and log data from other wells on and near the block, and facies interpretations were made for the ES4. At the same time, seismic isochron mapping of the ES4 interval was done to define the paleo-topography of the area. The integrated results of the evaluation suggest that rather than comprising one large, marginal lacustrine algal limestone build-up, as originally interpreted, the Yi64 Block ES4 reservoir comprises a series of small algal limestone build-ups which developed on small topographic highs in a patch reef-like configuration. The 1974 Well Yi64 discovery was drilled in the center of an ES4 build-up, whereas the 2001 Well Yi64-1 dry hole is interpreted to have been drilled on the edge of the build-up.