Dedicated to the art and engineering of pore pressure prediction and potential drilling hazards.
Issue Number 1
WELCOME to the premier issue of the Baird Petrophysical International, Inc. NewsLetter. This issue is dedicated to following individuals who are pioneers in the pore pressure prediction field:
Eugene S. Pennebaker Paul E. Pilkington Leo J. McClure
We hope you will join us in recognizing these individuals and the significant contribution they made to our industry. This newsletter will routinely contain articles written by several of these individuals especially for inclusion in this newsletter. Some will be regular contributors and some will be honored as guest writers. We think you will agree that they offer some valuable viewpoints and perspectives on the work that we are doing today.
This newsletter is designed for distribution by email and snail mail. This keeps our costs reasonable and insures timely delivery to you, while allowing you to easily enroll (and remove) your name from our distribution via our Internet Home Page. It further allows the recipients to easily comment on the contents of this publication. If you do not find this newsletter valuable and useful, interesting or anything else that would encourage your continued enrollment, please send us you comments as this is a work in progress and will improve and expand with time.
Figure 1. Eugene S. Pennebaker, Jr., Exxon Retiree, currently living in Corpus Christi, Texas. Visited by BPI staff, April 28, 2000.
Mr. Pennebaker contributed greatly as a pioneer to pore pressure prediction. While employed at Humble Oil (now Exxon Mobil) Pennebaker wrote the book on the utilization of seismic reflection data to identify and quantify abnormal pressure, drilling rate of penetration and especially the drilling parameters’ relationships to geologic age and seismic interval velocity. BPI and McClure and Associates jointly refined, re-defined and improved on the methods laid out by Pennebaker in 1965. Today with this first issue of The BPI Newsletter, we salute Eugene S. Pennebaker, Jr. for his contributions to drilling safety by use of pore pressure prediction. Please see article below by Leo J. McClure, History and Pioneers of Pore Pressure Prediction.
BPI NEWSLETTER will attempt to do some missionary work in the area of standards --- standards for terminology, standards of plotting, standards for interpretation processes, and standards in other areas that are common to pore pressure understanding. Presently there exist no standards and thus there is a lack of communication even within the pore pressure profession. This has specifically caused misunderstanding and results that have been subject to numerous misunderstood reports. We intend to propose BPI’s standards to the industry because we believe that these standards are both useful and necessary for the safety and efficiency of drilling of oil and gas wells. We will show how the more common tools, such as overlays and well-to-well comparisons, will be more universally applicable. This will lead to industry standards for this important wok, led by BPI’s leadership in this area. Due to the obvious lack of standards, we hereby solicit your candid comments and promise to address them in subsequent issues. The result of this effort shall be a recommended set of standard plotting scales and presentation formats. BPI will not let this issue rest without a recommended solution.
“Software is a tool and not a solution,” Jack D. Hall
“Computers, God’s gift to mankind?” Paul E. Pilkington
Electrical log pore pressure plotting started in the early 1960’s by using the old “Electric Logs” of that era. The resistivity curve value was plotted on single cycle semi-log paper with a depth scale of one inch equals 1,000 feet for depth and the resistivities plotted by ohms or tenths of an ohm across the top of the paper. This system worked fairly well until industry started drilling deeper wells such as 15,000 to 16,000 feet then the paper became ungainly long. Also the early clear plastic readers were very large and anything but easy to use to quantify the log resistivity readings. Some of the early men to experiment with this type of log plotting were Dr. C. E. Hottman and R. K. Johnson, Shell research and drilling personnel, and a few geologists in the New Orleans office of the old Humble Oil and Refining Co. which is today Exxon Company. Dr. W. E. Wallace, Forest Oil Company, published his ideas in 1964 and 1965 in the Oil & Gas Journal. W. R. Matthews and John Kelly, Mobil Oil Company, also were in the early pioneer group working on pore pressures from electric logs.
One of the pioneers on drilling problems in general and on pore pressure evaluation in particular was Eugene S. Pennebaker, Jr. He was employed by Humble in the south Texas Division in Corpus Christi. He did considerable work and research on seismic data to determine formation pressures before the well was drilled. This work was published in the SPE landmark paper #2165 entitled “An Engineering Interpretation of Seismic Data”. From his original study of 350 well velocity surveys or check shots, he developed several pressure readers. The first and one used in his paper was for use with seismic interval velocities; the second one was for use with the sonic log called an acoustic reader (or overlay). The one most used in South Texas was his conductivity reader developed for the Miocene Frio formation wells that Humble Oil was drilling on the King Ranch and adjoining leases at that time. In our practice we will use modifications of his acoustic and conductivity readers as well as other proven methodology.
Practical field interpretation of data is the main thrust of this newsletter and this column. Knowledge of certain geological principles and physical laws are helpful in the understanding of the science of abnormal pressure, but the actual interpretation of the drilling data generated at the wellsite is an acquired art based mainly upon experience. Therefore, this column is written expressly for drilling personnel --- roughnecks, drillers, toolpushers, drilling superintendents, engineers, geologists, service company personnel --- or any other person associated with boring a hole into the earth to find hydrocarbons.
Hopefully, this newsletter will give you the knowledge to recognize overpressured formations while you are drilling. And you can avoid fire, killed or injured persons, junked holes, severely damaged oil and gas reservoirs, and loss of time, equipment and money. Literally, you can Drill Abnormal Pressure Safely.
This newsletter is not a cook book for drilling a difficult, overpressured well. It does not replace common sense, sound reasoning, or proven detailed procedures for a specific job. Above all, the manual will not make you an instant expert on abnormal-pressure drilling; expert status is achieved only through extensive study and on-the-job experience.
You will learn some basics of how to predict, detect, and evaluate abnormally pressured formations, and how to solve the resultant drilling and casing problems.
Engineers and explorers working together can supplement conventional structural data with additional information derived from seismic structure maps, seismic velocity analysis, offset drilling data and wireline logs. These methods have been presented at various seminars for the past several years.
These methods involve using pressure, temperature, and wireline log data in addition to seismic mapping and velocity analysis. These methods can determine depth cut-offs, areas where modified seismic techniques may be required for seismic stratigraphy studies, and areas of poor source potential in overpressures. In addition, statistical analysis of probabilities of encountering sands with sufficient thickness and permeability for economic rates appear feasible.
Figure 2. Deep overpressured reservoirs fall into a temperature-pressure envelope.
Deep overpressured prospects have been evaluated for the past several years using the Timko-Fertl pressure-temperature chart shown in Figure 2. In all of the deep wells drilled into the temperature-pressure envelope area noted as aquifers, no commercial hydrocarbons have been encountered.
The chart shown in Figure 2 applies solely to clean Tertiary clastic sediments offshore Louisiana and Texas. It does not apply to areas offshore Texas where calcareous sands are found, because the consolidated sands can fracture and create additional storage volume. It does not apply to the deep Smackover and Norphlet areas, because generation and trapping mechanisms are different.
Pressures and temperatures can be estimated from seismic, drilling and wireline data. Seismic mapping and velocity analysis can be used to help extrapolate offset data into the proposed location.
This chart can be used within an area to determine the maximum depth cut-off’s for exploratory drilling and enable more effective use of the exploratory dollar. One major oil company completed a study about two years ago, which indicated one exception to the envelope from all deep Louisiana wells drilled to that date. It is reported to be slightly outside the line. However, my personal experience of monitoring drilling for 27 years offshore and making pore pressure plots for 35 years has failed to find the one well, which is reported to be the only exception.
Figure 3 illustrates the effect dipping beds have on pore pressure in abnormally pressured formations. Moving up-dip results in higher pore pressure gradient in mud weight equivalents (equivalent mud weight, or, EMW). This fundamental, simple relationship when used with seismic structural mapping, offset wells and seismic velocity analysis can help remarkably to estimate the expected pore pressure at the proposed well location. The same process works in reverse when you move down-dip.
Figure 3. Effect of dip on formation pore pressure.
Most of us have probably experienced the frustration and potential errors faced when trying to compare data from separate wells where the plots, data, scales and presentations all seem to collaborate to make the comparison either impossible or dangerously misleading. You may even have a desk drawer full of overlays, none of which seem to be on the scale and units of the data you are attempting to interpret. This column will discuss how some of these tools came to exist, why it is of extreme importance to have a semblance of standards, and how we are going to accept these standards.
The most basic area of standards is also the oldest—metric or Imperial (English) units?? Our industry has made a concerted and effective effort to move to the metric system used by most of the scientific and governmental world. But we have to realize we have left behind some important people who have either chosen not to commit to metric, or who may not have been provided the tools necessary to make this transition.
An ever present and important part of our work is our communications with the rig crew who are actually operating the rig and whose cooperation and input we desperately need to drill any well safely and efficiently. Many if not most of these personnel are not well versed in the metric system. If we are to communicate information to these critical personnel, we must do so in the terms they are most comfortable using. In most cases these are Imperial (English) units — i.e., lbs/gal, ft/hr, psi, pounds, or Tons. If any of these personnel happen to be uncomfortable with conversions, which BPI has actually witnessed, they may make a wrong guess, or translation, which could lead to serious, well control problems
BPI Newsletter is published monthly and freely distributed and copied by Baird Petrophysical Group, Inc., 1784 W. Sam Houston Pkwy N., Houston, Texas 77043-2723.
The results discussed herein are based on interpretation of drilling engineering, geological, geophysical and other scientific data supplied to Baird Petrophysical by its various customers on a private basis. It is the Reader’s responsibility to value its use. Baird Petrophysical specifically disclaims and does not warrant any of its news, comments, interpretations or opinions about the information presented here.
BPI Baird Petrophysical
1784 W. Sam Houston Pkwy N.
Houston, TX 77043-2723
Tel: (713) 461-1784
BPI Newsletter, by BPI Staff.
Simple Seismics, by Nigel Anstey.
Drill Abnormal Pressure Safely, by Leo J. McClure.
Shallow Seismic Safety Study, by Ralph W. Baird, et al.
Seismic Interval Velocity Analysis, by Leo J. McClure.
CopyrightÓ2000-2008 Baird Petrophysical Group, Inc.