Reservoir Management Makes a Marginal Field Fruitful in Bohai
Authors: Ge Lizhen , Yang QingHong , Fang Liwen , Zhao Chunming , Lizhen Ge , Qin Wei , Xu Yuxia , Li Tingli , Cheng Dayong , Tong Kaijun 
Published: May 2011

QHD32-6 is typical offshore heavy oil filed with about 1.1 BSTB of OOIP and with a very complex fluvial reservoir in Bohai Bay, China. The field was developed by CNOOC, Texaco and Arco in 1998. Based on the Original Field Overall Development Plan, the forecasted waterflooding recovery was about 17.4% OOIP due to the complex sand and OOWC, high crude viscosity and active bottom and edge water.

After starting production, the water almost broke through immediately in many producers and the oil production was disastrously declined. After two years operation practice, oil recovery was downsized to 13.4% in 2003. An integrated reservoir management program to improve oil recovery was initiated in 2003. The reservoir characterization was re-visited in detail with new data from development practices, infill well drilling, and dynamic production analysis. The comprehensive program was developed which including (1) water management; (2) infill drilling; and (3) EOR.

The key of water management is to control the rise rate of water cut. The program includes separated water, plugging sands with high water cut, maintaining reservoir energy by smart water injection, and injection profile improvement. The rise rate in water cut was significantly changed from 20% per year down to 3.5% per year.

Infill drilling was initiated in 2004 and is gradually and successfully expanded to the entire field based on the study of remaining oil distribution. So far, 36 out of 37 infill wells were added to production and showed a good performance.

For EOR practice, a field trial of cross-linked gel injection is implementing. The pilot test study of polymer flooding and N2 Foam flooding are conducting now.

QHD32-6 field has achieved a 0% of decline since 2006 and the production rate even jumped from 28,300 BOPD to 33,200 POBD in 2010 or increases 17.3%.

The forecast waterflooding recovery has changed to 24% based on the field operational practices. It indicates a good reservoir management can be a critical operation strategy to the marginal field development.

The successful application of reservoir management is leading the secondary development of this field. It is expected the EUR by the end 2030 by waterflooding and EOR processes will reach 35%. It provides a good example in Bohai Bay.

Introduction

QHD32-6 oil field1 is located in the center area of Bohai Bay, with 20m of average water depth (Fig. 1). It is a large heavy oil field discovered by CNOOC in 1995. The oil field is geographically divided into 3 blocks: North, South, and West block. QHD32-6 oil field produces from Minghua(Nm) formatiom and Guantao (Ng). Nm formation is fluvial depositional reservoirs with meandering channels, multiple sand systems and complex oil/water systems. Ng is a fluvial sand deposition with braided channels and strong bottom water. It is a typical heavy oil and can be characterized by the following properties. In the reservoir condition, oil has high density (0.903-0.926 g/cm3), high viscosity (43-260mpa.s), and low solution gas/oil ratio (13-24m3/m3). Reservoir porosity of Nm is 0.25-0.42, and permeability is 100-11487× 10-3µm2. Porosity of Ng is 0.25-0.43, and permeability is 500-18443×10-3µm2. The difference of formation pressure and bubble pressure is about 2-5MPa. There are complex oil water contacts in the reservoir.