Reservoir Management Using 3D Seismic Data
Authors: Robertson James D. 
Published: December 2007

Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering.

Introduction

The geologic detail needed to develop most hydrocarbon reservoirs properlysubstantially exceeds the detail required to find them. This obvious, butcompelling. precept has fueled the steadily increasing application ofthree-dimensional (3D) seismic analyses to reservoir management. A measure ofthe increase is that 3D surveys now account for half the seismic activity inthe offshore Gulf of Mexico and North Sea. and the percentage has risen yearlysince commercial 3D surveys were percentage has risen yearly since commercial3D surveys were first shot in these areas in 1975 (Fig. 1).

Likewise, 3D seismic surveying in other offshore areal. and on land isgrowing rapidly. My Fall 1988 SEG Distinguished Lecture addressed the generalsubject of managing reservoirs by use of 3D seismic data; this article isderived from that lecture. There are three parts to the article: a definitionof reservoir management; a discussion of the various kinds of 3D seismicanalyses that can affect the development and production of a field; and asynopsis of the history and production of a field; and a synopsis of thehistory and potential of the 3D seismic technique. potential of the 3D seismictechnique.

Definition

A good working definition of reservoir management is maximizing the economicvalue of a reservoir by optimizing recovery of hydrocarbons while minimizingcapital investments and operating expenses.

The first thing to note is that this definition is not geophysical orgeological; in fact, it's not even an engineering definition. Reservoirmanagement really is the economic process of raising the worth of a property tothe highest process of raising the worth of a property to the highest possiblelevel. We generally measure economic value by possible level. We generallymeasure economic value by yardsticks like present worth, investor's rate ofreturn, payout, and investment efficiency. The task is to maximize (minimize inthe case of payout) these economic descriptors. Economic value generallyincreases when more reserves are proved or when the reservoir's producing rateincreases. Of course, capital investments (drilling. seismic shooting. andlease bonuses) and operating expenses (lease rentals, staff costs, taxes, etc.)must be incurred to find and subsequently to develop and produce thesereserves, and these expenditures themselves detract from the economic value. The reservoir manager thus trades off expenditures that drain present worthagainst the chance of increasing present worth by adding reserves and/orincreasing production. The process is a continuous balancing act.

What is the role of seismic surveying. particularly 3D, in this balance? Basically, it impacts reservoir management in two different ways. First. a 3Dseismic analysis can lead to identification of reserves that will not beproduced optimally. or perhaps not be produced at all, by the existingreservoir management plan. Secondly, the analysis can save costs by minimizingdry holes and poor producers, by contributing to the proper sizing and designof facilities, and by condemning leases that can then be dropped to avoidrental payments and/or to take tax write-offs. These concepts are summarized inmy first major point: 3D seismic data contribute to reservoir economics byadding reserves and/or by reducing costs. Either of these impacts can besufficient justification for shooting a 3D seismic survey. Of course, the bestsituation is when both happen at once. and that is generally the case.

Process Model Process Model One possible model of the reservoir managementprocess. the linear system, is shown in Fig. 2. This model consists of thefollowing sequence: a discovery, an evaluation of the discovery, implementationof a development plan leading to production of the field, and final abandonmentwhen the field production of the field, and final abandonment when the field isno longer economical. In this scheme, a 3D survey is shot during the evaluationphase and is used to assist in the design of the development plan, after whichdevelopment and production start up. production start up. I suggest that thislinear model is not what really happens in reservoir management, except in thevery simplest cases (a discovery followed by one or two offsets that fullydevelop the reservoir). The real world generally is the process shown in Fig.3, called the iterative system. This model also starts with a discovery. butthen goes into a loop where data are constantly being evaluated to form thebasis for development/ production decisions (such as locating production andinjection production decisions (such as locating production and injectionwells, siting and designing platforms. setting flow rates, managing pressuremaintenance, performing workovers, planning waterflood and tertiary recoverystrategies, etc.). planning waterflood and tertiary recovery strategies, etc.). When implemented, the development and production activities in turn generatenew information (logs, cores, drillstem tests, pressure tests, etc.) thatchange maps, revise structure, alter pressure tests, etc.) that change maps, revise structure, alter the reservoir stratigraphic model, and so on. Most ofthe time spent in managing reservoirs really consists of going around thisloop. Occasionally, a deeper pool or offset extension test will spin off fromthe evaluation, resulting in a new discovery and revitalization of the loop. This process continues until the field is finally abandoned.

JPT

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