Meren Field-An Engineering Review
Authors: Poston Steven W. , Lubojacky Ronald W. , Aruna Mohammod 
Published: December 2007

This paper describes the engineering process required to formulate a comprehensive plan to deplete eight major oil reservoir units in the Meren field simultaneously. The multidisciplined effort involved computed log analyses, core analyses, material-balance studies, cross-sectional simulation studies, and simulation of certain reservoirs.

Computer simulation of candidate reservoirs indicated that the injection of water increased recovery to a greater extent than the injection of gas. The studies also verified that the reservoirs may be treated as homogeneous units.

Primary recovery was calculated to be 38% of the original oil in place (OOIP). The engineering study recommended that 200,000 B/D seawater be injected into the eight major reservoir units. Water injection would increase recovery from the Meren field by 121.7 million bbl oil. Ultimate recovery for the reservoir candidates would be increased to 48% of the oil in place (OIP).

Introduction

The Meren field is located in federal offshore waters off Bendel State, Nigeria. The water depth in the field varies from 48 to 60 ft. The field is owned jointly by the Nigerian Natl. Petroleum Corp. (NNPC) and Gulf Oil Co. (Nigeria) Ltd. (GOCON). The field was discovered in 1965, with first production occurring in Sept. 1968. Fifty-seven wells have been drilled in the field, three of which are dry holes. As of July 1, 1980, the field had produced 347,194,961 STB oil, 321,545,190 Mcf gas, and 10, 123, 132 bbl water.

The continued pressure decline during the producing life of the field prompted an in-depth investigation into the remaining potential. All major reservoirs in the field were found to have very low maximum efficient rates (MER's) in relation to the quantity of remaining reserves. The worst-case reservoir (Reservoir G1-G2/A) was found to have a producing life extending to the year 2010 at an MER of 4,000 BOPD. The installation of some type of pressure-maintenance project would accelerate field depletion to within a reasonable time frame.

A feasibility study was initiated on the Meren field in 1978 to determine the potential for improving the recovery. The study is reported in a companion paper (see Page 2095).

A generalized plan to deplete all candidate reservoirs in the Meren field simultaneously evolved early in the study. This type of field-depletion scheme appeared to offer a practical remedy to the following problems.The field production platforms and most of the well jackets had been set in the late 1960's and early 1970's in an offshore saltwater environment. Life of the physical plant was estimated to be approximately 30 years. Corrosion over such an extended time would require the replacement of the in-place field equipment.The individual reservoir MER's were too low to permit depletion of the majority of the reserves from the field within this physical-plant lifetime limit.The injection of water into the reservoirs in a sequential manner would increase recovery. but field life more than likely would extend beyond plant life.The value of the reserves would be negligible if they were discounted back to time of production.The installation of additional equipment in the Field would require the setting of another platform.

The capital requirements for a large injection station were not appreciably greater than those for a moderate-size injection station.

This paper describes the process of coupling the investigation into the rock and fluid characteristics of the field with field performance data. The product of these efforts was a plan to deplete all of the major reservoirs in Meren field effectively and simultaneously.

JPT

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