Summary

During the last half of 1995, a study was initiated to investigate the currently applied technologies used to predict, detect, and evaluate the magnitudes of abnormal pressure and fracture pressure gradients in the earth's crust. The main thrust of the study was to determine the methods most commonly used to calculate the pressures for well planning purposes as well as during actual drilling and post drilling analysis.

Following is a list of the main objectives of the study:

  1. A literature or document search was conducted, covering most all of the published papers written in English concerning these subjects. Over 250 documents, including those for new methods that oil companies and/or service companies have recently developed but remain unpublished, were reviewed. Many of these were summarized for ready reference.

  2. A direct interview survey was carried out with oil companies and service companies, after having supplied them a detailed questionnaire. The number of companies participating in the interviews reached 30 including international major oil companies, drilling contractor and service companies from the United States, Canada, and South America.

  3. Actual well and formation data were used to evaluate the most commonly used methods. Formation pore and fracture pressure gradients were calculated and plotted versus depth for several methods. These common methods, or techniques were determined statistically from the interview survey results.

Technical reasons for large deviations between calculated and actual measured pressure data were clarified, and both effectiveness and limitations of each method were evaluated.

Based on all the findings of this study, including the comparative calculations, the best approach was established for pore pressure and fracture pressure gradient prediction work. This procedure is included.

Introduction

In September 1995, Japan Petroleum Exploration Co., LTD., hereafter called "JAPEX", entered into a contractual agreement with Eaton Industries of Houston, Inc., hereafter called "Eaton", whereby Eaton was to conduct oil industry surveys of currently used technologies used to predict, detect and evaluate the magnitudes of abnormal formation pressure and fracture pressure gradients. The contract specified certain tasks to be undertaken by Eaton. These scope of work tasks were as follows:

  1. Conduct a literature search or document survey, by collecting and reviewing copies of all published papers on these subjects, restricted to those papers written in the English language.

  2. Conduct an interview survey, in the presence of JAPEX witnesses, with oil companies and service companies in the United States, Canada, and South America, to determine commonly used methods.

    Eaton was rired to mail a questionnaire to each company prior to scheduling an interview with each respective company.

  3. Perform a series of calculations for the top several methods that seemed to be effective. Actual well data were to be acquired by Eaton. Technical reasons of deviation from actual measured pressure data were to be clarified, and both effectiveness and limitation of each method evaluated.

These tasks were completed by the end of February 1996. Results of the study follow in the remaining sections of this paper, ending with a recommended approach for formation pressure predictive work.

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