Identifying Opportunities in a Complex Mature Oil Reservoir; a Company
Authors: Omara E.  A. , El hawary A. F. , Nosseir M. , Samieh A. , Baydoon M. 
Published: May 2016

This paper presents a case history of defining the field development plan for a complex; heavily faulted layered; undersaturated oil reservoir, with significant degrees of structural and production uncertainties. In such case, good reservoir management practices and reservoir monitoring are the main keys to understanding the reservoir behavior.

The reservoir has numerous challenges, which complicate reservoir management; like complex geology, pressure support for different layers, water injection optimization, scale depositions, and commingled production which introduces uncertainties regarding the production and injection contribution. This leads to difficulties to identify bypassed oil in the reservoir. Therefore frequent production logging, monitoring the producing water salinity, and key data from wells and RFT/MDT of the new infill wells were used for managing such uncertainties'. This served as primary keys to identify different vertical and lateral flow barriers, and was used as a basis for water injection optimization in such challenging conditions.

The reservoirs were studied by means of analytical methods and integration approach of wells' and reservoir surveillance data for understanding the structural configuration, investigate various production problems, optimize water injection strategy, and identify bypassed oil and poorly swept areas. The methods defined an extensive portfolio of infill drilling and other cost saving rigless activities to restore production potential of the field. This approach added about 22 MMSTB of oil reserves which represent 8 % increase in the ultimate oil recovery, and flattened the oil production for more than 5 years.

New infill wells were confidently identified to achieve all of the following objectives access bypassed reservesaccess attic oil reservesadding another drainage point to the existing producers.

The presented reservoir management practices has proven its ability to timely support the operational decisions, pinpoint infill wells, and prolong the life of a mature asset. It is not moving away from detailed dynamic model, but these practices are required in similar uncertainties conditions to develop right sense of understanding of reservoir behavior, and provide invaluable input data which adds credibility to the dynamic model.

Introduction

Ras Budran oil field, located in the northern Belayim offshore area; about 4 km west to Sinai Gulf of Suez coast (Fig. 1), is operated by the Suez Oil Company (SUCO). The field was discovered in 1978 by drilling the discovery well EE85-1 which penetrates several sand stone reservoir units extending over about 1800 FT to an original oil water contact at 12350 Ft. After discovery three appraisal wells were drilled with the objective of defining the field boundary and determine the total oil in place, and hence decide the commercial viability of the project. Subsequently the field has been developed from three small offshore platforms have a total of 29 slots.

The structural configuration of the Ras Budran field is a structurally complex pre-Miocene reservoir, severely strained by faults of different throws and aligned in various directions. The faults divide the reservoir to three main fault blocks, A-, B-, and C-Block (Fig. 2). The sedimentary sequence ranges from Paleozoic to recent. The main reservoirs involve Nubian C & D (Carboniferous and older), Nubian A (Carboniferous - Early Cretaceous), and Raha Sands (Cenomanian) (Fig. 3).