Design optimization of a horizontal well in thin oil column reservoir in Gulf of Thailand using experimental design methodology

Abstract

Horizontal wells have been drilled in the Gulf of Thailand since the late 1990’s to maximize oil recovery and prolong field life. Due to its complex geology, most of oil reservoirs have thin oil columns and are difficult to map. Decision to drill a horizontal well thus needs to compromise between pre-drill uncertainties and gain in benefits over traditional vertical or deviated wells. This research presents an application of experimental design methodology to optimize design method of a horizontal well in a thin-oil-column reservoir in the Gulf of Thailand. Petrophysical and engineering data from an existing horizontal well database was collated and statistically analyzed. Series of reservoir simulations on simplified reservoir models were conducted with respect to experimental designs to screen out significant factors and construct two proxy models. One is for predicting an ultimate recovery factor of a horizontal well. The other is for that of two vertical wells. By using the proxy models, a simple method capable of identifying thin-oil-column reservoirs which have high suitability for drilling a horizontal well is proposed. As a result, burden on reservoir modeling and simulation could be reduced. In addition, statistical analysis results of the designed experiments show that porosity, permeability, capillary effect, well standoff to oil-water contact, vertical thickness of oil column, liquid rate production control, a ratio of horizontal well length to reservoir length, and their interaction effects significantly influence ultimate recovery of the horizontal well.