Among the diverse roles EGI plays in ensuring energy security in the future is supporting and mentoring students—from undergraduate to Ph.D.—who are pursuing careers in the industry. Experienced, dedicated, and knowledgeable EGI scientists are mentoring and supporting the next generation of energy industry leaders.
This article highlights three students and the collaborative work they are doing under the guidance of advisors and mentors at EGI: Raili Taylor, Chemical Engineering; Manas Pathak, Chemical Engineering; and Dhrupad Raghuveer Beti, Petroleum Engineering.
Raili Taylor*, Department of Chemical Engineering, Ph.D. Candidate
Raili Taylor is currently pursuing her Ph.D. in Chemical Engineering. Her advisor is an EGI Affiliate Scientist and USTAR Associate Professor of Chemical Engineering, John McLennan. Raili has also participated in research with EGI’s Ian Walton and Joe Moore, who sponsored her participation in a conference last year.
Raili’s current research interest focuses on the potential for cement sheath degradation during routine pressure cycling, such as might occur during hard shutdowns, hydraulic fracturing, workovers, and routine production. Experimental and numerical work will highlight problems and suggest avoidance and mitigation procedures.
“Growing up in Utah, I enjoyed many outdoor activities such as hiking, backpacking, and camping. As a young adult I learned to ski, climb, and generally loved being outdoors. I gained a healthy respect for the environment and the treasures we have, especially in Utah” Raili says.
“Lately, climate change has come to the forefront and people are becoming more and more concerned with methane. Methane is a powerful greenhouse gas and can end up in the environment through natural causes, but can also end up in the environment from oil and gas wells. It is currently unknown how much methane escapes from oil and gas wells but literature estimates range from 0.5–11% of gas produced. Most wells have cement placed between the casing (steel pipe) and formation wall. This cement can become damaged from routine pressurization of the well, temperature changes, chemical damage and others factors allowing gas to escape. This is problematic on several levels as there are safety, economic, and environmental issues. My current research is focused on determining the mechanisms of cement damage from routine pressure cycling and how this translates into methane leakage. This research is important but does not complete the picture of all causes of leakage. I’d like to continue working on this problem as part of my career until we have a better understanding of how much methane leakage occurs from oil and gas wells.”
Cement Damage from Routine Pressure Cycling in Oil and Gas Wells
Cement is placed in wells between the casing (steel pipe) and formation wall to create a hydraulic seal between potential contaminants and the surface and/or groundwater. If the cement becomes damaged it can allow a pathway for gas to migrate to the surface. This is problematic on several levels since there are safety, economic, and environmental issues. From a safety perspective it can lead to loss of well control, or a blowout. Additionally, methane that is leaking and pooling can lead to an explosion if the concentration becomes high enough. This has been documented in gas storage reservoirs that have leaks in surface equipment as well as leaking wells. From a financial perspective, lost gas is lost revenue. It is also expensive to mitigate methane leakage and repair cement. Currently the most reasonable repair protocol is cement squeezing — a procedure that can cause a larger fracture with a relatively low success ratio. Remediation is also expensive, from the perspective of a workover as well as lost production while the well is shut-in. From an environmental perspective, natural gas is dominantly methane which is a substantially more impactful greenhouse gas than carbon dioxide. Over the last few years there has been extensive research on methane leaking from hydrocarbon fields. While there is no confirmed measurement of how much leakage is actually occurring, indications are that it serious enough that regulations will be impending; another significant driver for comprehending mechanisms and mitigation techniques. For instance many of the studies have ranged in estimates between 0.5–11% of gas produced. The 11% estimate comes from a study in the Uinta Basin, a potential problem of immediate concern to both the producer and local communities. Legacy wells with inadequate cementation are likely serious contributors, particularly when they were intended to isolate shallow, bypassed gas zones.
In order to solve the problem of methane leakage it is important to more precisely define the problem and the extent to which it exists. This involves characterizing how much leakage is actually occurring from faulty cement and what are the most common damage mechanisms.
Current Research Activity
Methane leakage from oil and gas wells can be divided into three types: short-term, medium-term and long-term. Short-term leakage occurs almost immediately after the cement is placed and usually relates to a formation pressure that is higher than the hydrostatic pressure exerted by the cement before curing. Using the correct cement density easily mitigates this scenario. Medium-term leakage usually occurs shortly after the cement has set and relates to fluid loss from the cement and consequent gas migration into the cement. As the cement gelation occurs bridging cement may no longer completely transmit hydrostatic pressure — at this point gas can displace the fluid in the cement, creating channels and tunnels. Most industry research has been on medium-term leakage. It is assumed that with good cementing practices and additives this should not be a problem. One can then speculate that long-term leakage may be the most significant consideration. The cement sheath, although initially weakened by voidage and channels that are ultimately connected to the surface due to aggressive service conditions – are in fact due to higher pressures from bypassed zones after abandonment.
Raili’s current research focuses on long-term leakage, which can occur weeks to years after cementing. Long-term leakage can be compounded cement damage due to pressure cycling, temperature variations, chemomechanical degradation and other variables. She is specifically looking at cement damage related to routine pressure cycling – during hydraulic fracturing down casing or hard shut-downs. Hydraulic isolation can be jeopardized from pressure cycling if the cement sheath debonds and a microannulus is created. The cement can crack (most likely tensile fractures) and can separate from the formation (usually only a problem if a large mud cake is left behind). There is also concern that the formation itself could be damaged with microcracks from drilling, thus allowing gas leakage.
At the outset, Raili worked with Randy Nielsen, a senior engineer at TerraTek, a Schlumberger company. They designed an “index test” to assess the potential for cement degradation due to cyclic loading. The purpose of the index test was to develop a simple test that could be used to quickly determine the stability of any cement/rock system without using a pressure vessel.
The next stage of testing involves designing and using a medium-scale pressure vessel to simulate a cemented wellbore and the surrounding environment. Surrogate cemented “casing” will be cyclically pressured. Concurrently gas will be flowed through the cement to detect changes in the permeability of the cement when degradation occurs. The cement will then be evaluated with computerized tomography. Variations of this test are desired as well such as with a mudcake, etc.
Raili will assess methods to prevent leakage and/or remediate the cement, ideally identifying a more effective method than “squeeze cementing.” Working with Prof. Amanda Bordelin, Civil and Environmental Engineering, several unconventional solutions have been suggested. There has been some exciting work on encapsulating bacteria in the cement that become active if it a crack forms. The bacteria would then seal the cement. Other more standard remediation or mitigation could include newer resins and other sealants. Raili notes that “there may not be a ‘one-size-fits-all’ solution; it may take several solutions to solve the problem.”
“I am interested in solving the disconnect between industry and the public through transparent communication. Currently, the general public has plenty of misinformation about the energy industry and this is perpetuated by lack of transparency from the oil and gas industry. There is also a disconnect between the energy people use in their daily lives and where it comes from. In other words the general public doesn’t understand where their energy comes from or how much they rely on it. This causes innovation and progress to slow to a halt. I believe it is important to provide education to the general public about energy and provide clear communication from industry to effectively solve current and future energy and environmental problems.”
*Energy & Geoscience Institute (EGI) Fellowship recipient
Manas Pathak*, Chemical Engineering, Ph.D. Candidate
Manas Pathak has been associated with EGI for more than two years, first visiting EGI in the summer of 2012 for an internship in which he worked on developing a geologic model for the Eagle Ford Shale Play. During that initial stay, Manas worked closely with Drs. Milind Deo, Bindra Thusu, and Sudeep Kanungo. He also contributed to laying the foundation for Indian Subcontinent Shale Resource Plays, Phase 1. This short visit was followed by a Graduate Research Assistant position one year later in the fall of 2013. Since joining the University of Utah as a Ph.D. candidate in fall 2013, Manas has been working with Dr. Milind Deo, EGI affiliate scientist and Chair of the University of Utah’s Department of Chemical Engineering and in close association with EGI Director Dr. Raymond Levey. Currently an EGI Fellowship recipient, Manas holds a Master’s degree in Applied Geology and has produced interdisciplinary research in reservoir geoscience and engineering—closely matching a number of EGI research objectives.
Manas’s research has focused on geologic controls on production of shale play resources. He is presently working at both basin and nano scales attempting to model different geologic processes that play a role in retention of hydrocarbons in tight rocks. He intends to build upon his Ph.D. research work to tie the nano scale investigation with the reservoir characterization of tight rocks with an eye to using his substantial skill and experience to further contribute to the exploitation of unconventional shale play resources.
Manas was a recent contributor to the URTec Conference held in Denver in 2014, where his presentation was extremely well attended and well received by the large audience.
*Energy & Geoscience Institute (EGI) Fellowship recipient
*President, Air & Waste Management Association (Student Chapter) University of Utah
*Vice President, Society of Petroleum Engineers (Student Chapter) University of Utah
Dhrupad Raghuveer Beti, Petroleum Engineering, M.Sc. Candidate
Dhrupad Raghuveer Beti is a graduate student at the University of Utah, currently pursuing his M.Sc. in Petroleum Engineering—a unique program offered collaboratively between EGI and the University’s Department of Chemical Engineering. Dhrupad’s undergraduate background is in chemical engineering.
He is also working as an EGI Research Assistant in Petroleum Systems and Geochemistry. He has previously worked on source rock analysis using Rock Eval Pyrolysis and Vitrinite reflectance.
Dhrupad’s current research work involves experimentation in pyrolysis using HAWKTM (Hydrocarbon Analyzer with Kinetics) specialized equipment recently acquired by EGI and interpreting the data from Pyrolysis, XRD, QEMSCAN® & Vitrinite Reflectance to better understand source rock characteristics. He is working closely with David Thul on the South American Shales, Phase 2 project as well as the iCORDS™ South Atlantic Margin research.
Working at EGI has been “one of the most enriching experiences” for Dhrupad. He notes that the opportunity to work with the HAWK™ analyzer is an uncommon opportunity for students because the machine is one of the most exclusive (only 12 in the world) and advanced tools for source rock analysis. He also values working with experienced professionals like David Thul, saying it “is the most insightful and knowledge building experience so far. As a Petroleum Engineering student it intrigues me to know the amount of background work that goes into exploration as a precursor to actual drilling.” Recognizing the value in working directly with scientists and mentors, Dhrupad feels it is a “huge advantage to understand Petroleum Geoscience through my research and simultaneously learn the different engineering problems faced by the industry from the courses in my degree program. This gives me a broad interdisciplinary perspective on the operations in the E & P sector.
“As a result, I am presently working on my thesis in which in I am trying to understand the composition of the hydrocarbons in the reservoir by altering some parameters involved in pyrolysis. This will help in understanding the reservoir and interpreting the well logs better.”
In the near future Dhrupad intends to concentrate on the petro-technical side of Reservoir or Production Engineering.
“I strongly feel that my present research will provide enough exposure and knowledge progress as an Engineer in the E & P sector. Also, access to EGI’s vast database, which is a result of contributions of many researchers, gives me a great advantage in learning from the different works of eminent scientist and researchers who have worked at EGI over the period of four decades” he says.
Raili Talyor, Manas Pathak, Dhrupad Beti, and Dr. John McLennan contributed to this article.