A Laboratory Study of Combustion Override Split-Production Horizontal Well (COSH) Process
Authors: Bagci S. , Aybak T. 
Published: March 2010

A 3D physical model has been developed to investigate the Combustion Override Split-Production Horizontal well (COSH) process. The 3D model is a rectangular box with dimensions of 18 cm by 54 cm by 12 cm. The vertical well was used as an air injection well and the top horizontal well was used to collect the gases generated by the combustion process. A horizontal production well was placed near the base of the model to collect hot crude oil and water. A total of eight experiments, six of dry combustion and two of wet combustion were conducted to investigate the process parameters.

Forty-eight thermocouples were used to obtain 3D temperature profiles in the vertical and horizontal mid-planes. Combustion peak temperatures up to 450? C were recorded, with oil recoveries exceeding 40% OOIP for the single vertical producer well case. The recovery using a horizontal producer placed at the base of the model was 65% OOIP, higher than the vertical producer.

The COSH process was performed to combine the beneficial features of gravity drainage and horizontal production wells. A hot gas chamber was formed around the vertical injection well similar to the steam chamber in the SAGD (Steam Assisted Gravity Drainage) process. In the COSH process the hot gas chamber consisted of steam, injected gas, and combustion gases. Gravity drainage was the principal mechanism for moving heated oil to the horizontal production well in the COSH process.

Introduction

In-situ combustion is a commercial process for recovering heavy oils. In this process, air or more generally an oxygen containing gas is injected into a formation containing viscous oil. A burning front supported by air injection is created and subsequently propagated through a reservoir. The burning front travels in the same direction as the injected air (forward combustion) or counter to the direction of air (reverse combustion). The high cost of air compression for dry forward combustion is one of the major factors that influences the economics. Therefore, the oil industry introduced a new concept that is water injection with air into the reservoir to improve the thermal efficiency of the process. Another important advantage of wet combustion is less fuel consumption compared to dry combustion.

The technology of horizontal wells for the production of crude oil from conventional and heavy oil reservoirs and tar sands has been implemented successfully in many fields. Extensive work has been carried out to develop horizontal drilling techniques to increase direct contact between wellbores and pay zones in order to improve productivity and recovery. Thin reservoirs, reservoirs with vertical fractures and in reservoirs where low productivity has been observed with vertical wells, due to water or gas coning positive results and improved recovery is provided by the application of horizontal well technology.

Until now, most laboratory experiments of in situ combustion have been conducted using combustion tubes whose results are then used for field applications. The two important parameters that must be understood before field application, are sweep efficiency and combustion front stability, which cannot be obtained from combustion tubes due to their one dimensional geometry.