Abstract

We describe an approach for estimating the reservoir potential by integrating multiple attributes derived from various input sources. We present both a simple heuristic method and one based on fuzzy logic, and show the two are effectively identical. Both methods can be implemented in the forward sense (without utilizing knowledge from existing wells) or the inverse sense (using existing well information to condition the final outcome). We applied the method to assess the reservoir quality throughout the Haradh area of the Ghawar Field of Saudi Arabia and evaluated the validity of the study by analyzing the outcome of wells drilled on the basis of this analysis.

Introduction

For optimal placement of a development well, a decision-maker is faced with a multitude of attributes - geophysical, geological, or engineering - that have varying degrees of confidence and that are related to the drilling objective in varying extents. These attributes are oftentimes large in number; thus, qualitatively assessing their relative impacts on the development problem can be laborious, subjective, or worse, erroneous. Sometimes they are incomplete or even contradictory in their inference to the expected reservoir quality. None of them, singly and separately, predicts the occurrence or amount of hydrocarbon-bearing reservoir with such an overwhelming confidence that precludes the need for the others. In reality, each attribute may sense the same or a different reservoir property than another. Therefore, it is the combination or integration of these attributes that yields a more reliable indicator of reservoir quality than any single attribute can.

The goal then is to integrate a multitude of fragmented pieces of knowledge derived from various input sources to come up with a single number at each location in the field that is indicative of the reservoir potential at that particular location. In addition to furnishing an accurate means of assessing the reservoir potential at any point in the field, this approach also provides a permanent record of why a particular location was selected over another, what pieces of information (attributes) entered into the making of that decision, and to what extent each of these attributes influenced that decision. In effect, then, this approach renders the entire decision-making process more objective and more open, and makes it quite facile and convenient to revisit that process after the well has been drilled to assess the decision and re-evaluate the contribution of each of the attributes into that decision - and perhaps readjust those contributions to fine-tune the method to yield a more accurate estimate of the reservoir potential for further wells to be drilled.

In this paper, we first describe a heuristic method of integrating these multiple attributes to estimate the reservoir potential. Then, we

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