Environmental Aspects of Oil and Gas Production

J. O. Robertson, G. V. Chilingar

• Publisher: Wiley-Scrivener
• Year: 2017
• Print ISBN: 9781119117377
• eBook ISBN: 9781119117391
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Energy

Oil and gas still power the bulk of our world, from automobiles and the power plants that supply electricity to our homes and businesses, to jet fuel, plastics, and many other products that enrich our lives. With the relatively recent development of hydraulic fracturing ("fracking"), multilateral, directional, and underbalanced drilling, and enhanced oil recovery, oil and gas production is more important and efficient than ever before. Along with these advancements, as with any new engineering process or technology, come challenges, many of them environmental.

More than just a text that outlines the environmental challenges of oil and gas production that have always been there, such as gas migration and corrosion, this groundbreaking new volume takes on the most up-to-date processes and technologies involved in this field. Filled with dozens of case studies and examples, the authors, two of the most well-known and respected petroleum engineers in the world, have outlined all of the major environmental aspects of oil and gas production and how to navigate them, achieving a more efficient, effective, and profitable operation.

This groundbreaking volume is a must-have for any petroleum engineer working in the field, and for students and faculty in petroleum engineering departments worldwide.

Chapter 1
Environmental Concerns

1.1 Introduction

This book is a systematic evaluation of surface and subsurface environmental hazards that can occur due to the production of hydrocarbons and how these problems can be avoided. The importance of such a study is dramatized by recent examples that have occurred within the Los Angeles Basin, CA:

1. In the early 1960s, a portion of the Montebello Oilfield developed in the 1920s was converted to the Montebello Gas Storage Project, under the City of Montebello (a city within Los Angeles County). A minimal amount of work was done on the older wells to prepare the wells for repressurization. In the early 1980s, significant gas seepages were discovered alongside and under homes from several prior abandoned wells. Homes were torn down to allow a drilling rig to reabandon the leaking wellbores which were endangering the community with migrating gas. These home sites were then converted to mini-parks so that future casing leaks could be resealed if necessary. These problems led to the abandonment of the gas storage project in 2000.
2. On December 14, 1963, water burst through the foundation of the earthen dam of the Baldwin Hills Reservoir, CA, a hilltop water storage facility which had been weakened by differential subsidence. This facility was located in a square-mile of metropolitan Los Angeles, CA, consisting of a large number of homes, of which 277 were damaged by moving water and inundated with mud and debris, or destroyed. Hamilton and Meehan (1971) noted that differential subsidence was a result of fluid withdrawal from the Inglewood Oilfield and the subsequent reinjection of water into the producing formation (for secondary oil recovery and waste water disposal). This resulted in the differential subsidence that was responsible for the ultimate demise of the earthen dam (see Chapter 3).
3. On March 24, 1985, migrating subsurface gas filled the Ross Dress for Less department store in the Fairfax area of Los Angeles. There was an explosion followed by a fire, due to a spark in the basement of the store. Over 23 people were injured and an entire shopping center was destroyed. The area around this center had to be closed down as migrating gas continued to flow into the area, burning for several days through cracks in sidewalks and around the foundations. This site was located directly over a producing oilfield containing many abandoned and improperly completed wells (see Chapter 2).
4. On October 23, 2015, massive volumes of escaping methane gas from a well (SS-25) in the Aliso Canyon Underground Storage facility reservoir flowed out and spread over the surrounding community of Porter Ranch, Los Angeles County, CA (Curwen, 2016). Engineers suspected that the escaping gas was coming from a hole in the 7-in casing about 500 ft below the surface. Therolf et al. (2016) reported the concerns of California Regulators to delay plans to capture and burn the leaking gas that had sickened and displaced thousands of Porter Ranch residents. The Aliso Oilfield was developed in the late 1930s and a portion of this oilfield was converted to a gas storage reservoir. The oilfield had previous fires from leaking wellbores that were put out by Paul “Red” Adair in 1968 and 1975 (Curwen, 2016). The escaping gas flowed into the nearby community for over 3 months, endangering the residents with health, fire and possible explosion hazards. At the time of writing of this book, the well has not been repaired.

Unfortunately, many oilfields located in urban settings similar to that of the Los Angeles Basin, CA, have been managed by catastrophe rather than through preventative management.

The objective of this book is to identify the environmental problems associated with the handling of hydrocarbons and suggest procedures and standards for safer operation of oilfields in urban environments.

This book is intended to help evaluate hydrocarbon production operations by looking at specific environmental problems, such as migrating gas and subsidence. The writers recommend a systems analysis approach that is supported by a monitoring program. Today there are many wells over 50 years of age and some over 100 years. The capability of these older wells to isolate and contain hydrocarbons decreases with time as the cement sheath deteriorates and the well casing corrodes. Chapter 3 describes the breakdown process of the cement in the wellbore with respect to time, resulting in the decrease of the ability for cement to isolate the reservoir fluids. Chapter 6 reviews the corrosion that can result in gas leaking holes in the casing. Thus, increased pressure by water injection, at a later date in the life of an oilfield, can create an environmental hazard in areas that contain wells with weakened cement and corroded steel casing, or inadequately abandoned coreholes and oilwells.

The intent of the writers is also to identify and establish procedures and standards for safer drilling and production of oilfields within the urban community. A necessary adjunct to these procedures is the establishment of a monitoring program that permits detection of environmental problems before occurrence of serious property damage or personal injury. This includes the following:

1. Monitoring of wells for surface seepage of gas.
2. Monitoring for surface subsidence.
3. Recognition of the oilfield geologic characteristics, including fault planes and potential areas and zones for gas migration to the surface.
4. Establishing procedures for the systematic evaluation of the integrity of both producing and abandoned oilwells and coreholes.
5. Monitoring of distribution pipelines and frequent testing for corrosion leaks.

1.2 Evaluation Approach

This evaluation approach requires development of a functional model for each oilfield operation. This approach should identify the basic hydrocarbon drive mechanism that is responsible for the movement of hydrocarbons in the reservoir. Particular attention should be given to faults and the caprock of the reservoirs.

Emphasis should be placed on the individual well production history, i.e., gas/oil ratio, water production and pressure history. Frequent surface soil gas tests should be made for all wells 50 years of age and older.

In gravity drainage pools, oil moves downdip and gas moves updip. As the gas/oil ratio of updip wells increases, these wells are shut-in. Most of the production occurs at practically zero pressure in gravity drainage pools. Freed gas, which accumulates at the top of the structure and is no longer held in solution becomes available for migration. If there is a pathway for its migration toward the surface or if such an avenue is created, it will migrate to adjacent areas of lower pressure working its way to the surface. The freeing of solution gas substantially increases the volume of gas available for migration.

If this migrating gas encounters a fault (natural path) or a wellbore (man-made path), it can then move toward the surface. As also pointed out in Chapter 2, as the wells age the casing corrodes and the cement fractures enlarge. The reason that cement ages and develops fractures with time is hydration of the cement. The cement does not have the same capability to isolate the hydrocarbons that it did when first put in place. This is contrary to a mistaken belief by many, that the risk of gas seepage is reduced over time as the reservoir pressure declines through fluid production. There are many older wells, drilled and completed 50 to 100 years ago within urban settings that leak.

1.3 Gas Migration

The existence of oil and gas seeps in oil-producing regions of the world has been recognized for a long time. For example, Link (1952), then the Chief Geologist of Standard Oil Company (NJ), wrote a comprehensive article on the significance of oil and gas seeps in oil exploration. In this publication, he documented oil and gas seeps located throughout the world. Although the primary purpose of Link’s paper was to identify the importance of surface oil and gas seeps in the exploration and location of oil and gas, it is of no less importance in identifying the hazards associated with the seepage or migration of hydrocarbons to the surface.

Various state agencies have published maps identifying seepage of oil and gas. For example, the Division of Oil and Gas of the State of California has published a detailed listing of seepages located throughout the state of California (Hodgson, 1987).

Many of these seeps are located in or near the immediate vicinity of producing or abandoned oilfields. As pressure drops, gas comes out of solution, allowing the freed gas to migrate toward the surface.

About 90% of all oil and gas seeps in the world are associated with faults, which provide natural pathways for migration of gas. Man-made pathways (wellbores) may be also present.

1.3.1 Paths of Migration for Gas

Fault planes and wellbores can serve as conduits for migration of gas from the oil/gas reservoirs to the surface (see Chapman, 1983; Doligez, 1987). Consensus of opinion, up to the mid-1960s, was that faults generally act as barriers to petroleum or water migration. Obviously faults acted as traps for oil/gas accumulations. The authors believe that, at best, faults are “leaky” barriers and that at a minimal differential pressure of 100–300 psi there is a flow of fluids across the fault planes. Thus, evaluation of fluid flow along (and across) fault planes is an important consideration, especially when monitoring for surface seepage.

The identification of potential paths of migration (fault planes and/or wellbores) within the geologic setting of any oil or gas field is essential in establishing the surface locations where seepage monitoring stations ought to be established. Also of importance are those locations where subsurface fault planes intersect water aquifers. Jones and Drozd (1983) pointed out that there is little doubt that faults can provide permeable avenues for hydrocarbon migration.

It is important to establish sampling intervals for a gas seepage monitoring program. When the flow of fluids is variable, a continuous monitoring system is required to obtain valid results. If only isolated samples are sporadically collected, the result may be a failure to detect a hazardous condition.

Usually, fluid movement along the faults increases their permeability. Following the San Fernando, CA, earthquake of February 9, 1971, it was recognized that seismic activity could not only damage wells, but also “trigger” the migration of oil and gas to the surface (Clifton et al., 1971). In conclusion, the mapping of surface faults is essential.

1.3.2 Monitoring of Migrating Gases

Measurement instrumentation and gas sampling procedures need to be considered for the reliable determination of gas seepage hazards. The objectives to be achieved are: (1) gas identification and source determination, (2) seepage pattern characterization, and (3) long-term gas sensing for detection and warning.

That distinction is important because the instrumentation and measurement techniques are different for each of the above functional areas. Natural gas found in an oilfield environment contains primarily methane and small amounts of ethane, propane, isobutene and other higher-molecular-weight hydrocarbons. The mere presence of these higher-MW hydrocarbons establishes that the gas is of a th...

Table of contents

• Cover
• Title page
• Copyright page
• Dedication
• Acknowledgments
• Chapter 1: Environmental Concerns
• Chapter 2: Migration of Hydrocarbon Gases
• Chapter 3: Subsidence as a Result of Gas/Oil/Water Production
• Chapter 4: Effect of Emission of CO2 and CH4 into the Atmosphere
• Chapter 5: Fracking
• Chapter 6: Corrosion
• Chapter 7: Scaling
• Appendix A
• About the Authors
• Author Index
• Subject Index
• End User License Agreement