Reservoir Fracture Characterization and Modeling in a Shuaiba Reservoir
Authors: Corbeanu R. , Nasoetion S. , Yang K. , Labiadh M. , Narayanan R. , Mubarak M. , Habib K. 
Published: March 2015

Massive mud losses, well logging, seismic data together with observed conformance issues and significant variation in well performance suggest a well developed fracture system in a regional Shuaiba reservoir. Proper characterization of such fractures plays a critical role in modeling reservoir fluid flow and production.

Fracture corridors are the dominant fluid flow paths in Shuaiba reservoirs and are the focus of this study. Their spatial distribution and conductivity are characterized by integrated analysis based on drilling, logging, core, seismic, and well performance. Geological analysis, including tectonic/structure history, strain/stress variation, and rock mechanical stratigraphy are performed to better understand the fracture system.

Overall well performance is clearly related to fracture distribution throughout regional fields. During early stages of production, before water flooding, conductive fracture corridors connected the underlying aquifer to producers and occasionally resulted in premature water breakthrough in high strain areas. Following the implementation of water injection, these fracture corridors also connect some injectors and producers. As a result, continued development requires recognizing and mapping these fracture corridors. This is done by acquiring saturation data in recent horizontal wells. Together with borehole image data, the width and configuration of fracture corridors can be characterized.

A practical approach is taken in 3D fracture modeling. Fracture corridors are interpreted in 3D by integrating all static and dynamic data available. Their conductivity is classified into high, mid and low using dynamic data and mud losses. Fracture distribution and flow properties are related to or constrained by geologically more predictable attributes including reservoir curvature, current day stress field, structure pattern, and mechanical stratigraphy.

Using the approaches described above, an improved characterization of the fracture system was developed and exported to a geologic model for use in a dynamic simulation model to better predict waterflood performance.

Introduction

A producing oil field, located offshore Qatar, was discovered and began producing oil in the early 1960s. Shuaiba deposits consist mainly of microporous mudstones and wakestones with a small percentage of grain-dominated rocks localized in shoals along northwestern area of the field. Current Shuaiba oil recovery is relatively low due to low rock matrix permeability, which is complicated by a system of fracture corridors that led to early breakthrough and early well abandonment in some areas of the reservoir.

Conductive faults and fractures have long been known to be important factors to fluid flow in Middle East Shuaiba Reservoirs. Studies have documented the evidence for fluid flow in conductive faults based on the results of petrophysical logs and well production performance. Of the 16 early Shuaiba wells in the field, three wells produced the majority of the Shuaiba oil. These three wells are located within or in close proximity to mapped fault zones.