Unconventional Recovery Research Articles

Pore-scale numerical investigation on spontaneous imbibition in natural fracture with heterogeneous wettability using the volume of fluid method

Understanding the spontaneous imbibition in the natural fracture with heterogeneous wettability is crucial for predicting and mitigating the impacts of unstable displacement on unconventional recovery. In this paper, the fracture structured mesh model is reconstructed based on the micro-computed tomography (micro-CT) image of naturally fractured tight sandstone. The mineralogy map-based modeling method for heterogeneous-wetting fracture is developed by combining the thin section images, X-ray diffraction (XRD) analysis, and multiple point statistics method. The simulation of the single-phase flow is performed to test the mesh independence. The effects of gravity and wettability on spontaneous imbibition in natural fracture and corresponding imbibition front dynamics are analyzed and discussed using the volume of fluid (VOF) method. The results show that (1) The structured mesh reconstruction method proposed in this paper can more effectively preserve the fracture structure compared to the unstructured mesh reconstruction method. (2) Gravity has a negligible impact on the pore-scale spontaneous imbibition in natural fracture. Under homogeneous-wetting conditions, spontaneous imbibition in natural fracture consistently exhibits stable displacement without significant residual gas formation. However, under the heterogeneous-wetting condition, the spontaneous imbibition displays typical capillary fingering, resulting in approximately 24.04% of the gas being trapped after spontaneous imbibition. The residual gas trapping mechanisms mainly include adhered, isolated, and connected gas. (3) Under both homogeneous- and heterogeneous-wetting conditions, the imbibing water saturation and the length of the imbibition front are proportional to the power of imbibition time during spontaneous imbibition in the natural fracture.

Independent and major equity market and commodity return sources around the time of hydraulic fracking and horizontal drilling revolution: a differences-in-decompositions approach

ABSTRACT Fracking and unconventional drilling have revolutionized international oil and natural gas production. Fracking increases the likelihood of well completion and decreases oil and gas equity and commodity market risk. Oil and gas Majors are producers with the greatest time and liquidity in the industry and are the largest integrated producers. Independents are smaller upstream, midstream, and downstream producers that have different capital and infrastructure and are less liquid than Majors. The fracking and unconventional recovery transition decreased returns to Independent equity market returns more than the Majors equity market decrease. Major oil returns increased with the transition by more than Independents. Independent equity returns across groups were higher after the transition than Majors both across and within groups. Fracking technology increased the likelihood of successful well completion, and with lower financial market risk, equity returns decreased in the post-fracking period.

Big Fracs That Add More Oil May Also Mean More Water, and That Can Be All Right

A few years ago, Occidental Petroleum managers were puzzled by why their recent Permian Basin wells were producing more water per barrel of oil, so they asked some engineers to figure out what was wrong. Their concern was understandable. While the company’s well evaluation system was supposed to screen out prospects likely to become big water producers, the amount of water flowing out of wells in the Delaware Basin drilled after 2018 far exceeded volumes from previous years. “We found that newer wells had a steeper increase in water cut over time than older wells,” the coauthors of an Occidental paper wrote about the work done to answer the question. They added, that “pre-2018 wells had an average water cut increase of 4% in the first 300 days (after cleanup) and then stayed relatively flat after 300 days, whereas post-2018 wells’ water cut increased at an average of 12% in the first 300 days and 16% in the first 600 days before reaching a plateau” (URTeC 3720245). Those trends, plus wells ultimately reaching an 80% water cut, suggested that a string of wells may have been drilled into water aquifers. While that is a risk in the Permian, the evidence suggests that the geology in the wells they compared was similar before and after 2018, even though the water cut levels were not. A big difference was how the wells were fractured. In 2018 Occidental began doing bigger fracturing jobs, using more water and sand per foot, which increased the number of stages and fracturing clusters. Those changes added oil production because “high conductivity speeds production and enhances the well’s net present value,” said Samuel Amadi, a senior reservoir engineering advisor for Occidental, while presenting the paper at the recent Unconventional Resources Technology Conference (URTeC). Based on production records, the water/oil ratio also was higher. Using data from comparable wells before and after the completion design changes, a model was created that quantified the relationships between fracturing designs and the oil, water, and natural gas flowing out of Occidental wells. “One recurring observation in all these completion scenarios is that a better-completed well will have higher fluid withdrawal and a steeper water cut trend after cleanup than a poorly completed well for the same reservoir and operating conditions,” the paper’s authors wrote. A coauthor, Xueying Xie, principal and manager of unconventional recovery design at Occidental, added that based on her team’s simulations, “we know we are not doing something wrong. This is doing a better job. It speeds production.” But unlike a well drilled through a fault connecting it to an aquifer, there was a limit to the water produced from these extremely tight formations. Like the oil production in more aggressively completed wells, the water production peaked at a higher level than the less intensely fractured wells but declined over time to a similar level. “On the water production side, just the pace changes,” Xie said.

Conventional and unconventional recovery of inulin rich extracts for food use from the roots of globe artichoke

Inulin is a prebiotic, recovered from several vegetable sources, used for its health-promoting and technological properties. In this study, inulin was extracted from artichoke roots, an emerging agricultural waste, using both hot-water and ultrasound-assisted extraction. Roots from five cultivars grown in three different sites were submitted to both hot water extraction and ultrasound-assisted extraction. Physic-chemical characterization of the extracts was carried out, and gelling and prebiotic properties were evaluated. The extraction yields of the artichoke roots ranged between 6.5 and 20.9 g 100 g−1, and the use of ultrasound led to an increase in yield only for two cultivars. The FT-IR spectra of the extracts were comparable to that of commercial inulin from chicory, whereas the average degree of polymerization was higher (32 DP). Furthermore, extracts provided gels with different hardness. In most cases, the ultrasound-assisted method increased the protein residue of extracts and reduced the antiradical activity and the gel hardness. The evaluation of the prebiotic properties showed that almost all the tested probiotic strains were able to grow on artichoke inulin although with different extents. The results of this study suggest that artichoke roots can be a suitable source of inulin, though the extraction technology, the genetic and pedoclimatic variables can severely affect yields, gelling properties and prebiotic activity of inulin extracts.

Poroelastic stress changes associated with primary oil production in the Los Angeles Basin, California

While recent investigations of induced earthquakes have focused on earthquakes associated with wastewater injection and unconventional recovery methods, the potential for earthquakes to be induced by primary production has long been recognized. We use boundary element methods to quantify the predicted geometry and amplitude of stress and strain changes associated with removal of large volumes of fluids in poroelastic reservoirs, focusing on the Los Angeles Basin (LA Basin) in California. We show that significant stress perturbations (upward of 0.1 MPa), while localized, typically extended several kilometers away from production horizons by the early 1940s. By this time, production horizons in the southwestern LA Basin were 2–4 km deep; models thus predict that stress conditions would have been perturbed significantly on faults at the upper edge of the seismogenic brittle crust, typically around 6 km. Predicted stress and strain changes associated with oil fields in the southwestern LA Basin during the first half of the 20th century, combined with stress changes caused by the 1933 Long Beach earthquake, could plausibly have induced a number of moderate-to-large earthquakes between 1932 and 1944. The rate of earthquakes in the southwestern LA Basin has been significantly lower since 1945 than it was for the three decades prior to 1945. We conclude that while decreasing production and pore-pressure reduction contributed to the initial decline, the continued decline was due in part to the advent of widespread water-flooding methods that maintained subsurface reservoir pressures.

Technology Focus: Gas Production Technology (November 2008)

Technology Focus One trend that Stephen Norris noted in his Unconventional Recovery editorial (JPT, July 2008, page 74) is that resources that have been on someone's back burner for 17 years (in the case of the Barnett shale) have finally started to have their day in the sun. What has changed? Did a new technology suddenly change all the drivers? Did incremental adjustments in existing technologies, or cross pollination from other disciplines, or an excess supply of technical talent make the difference? How about the value of the underlying product? Until approximately 10 years ago, gas was viewed in many parts of the world as a waste product and was flared. Now, worldwide natural-gas prices make it possible to go to extraordinary efforts to bring gas to market. Classic economic theory predicts that as prices increase, high technology and high-cost supplies will, eventually, join the market, and as long as they do not overwhelm it, will become a long-term source and drive the price back to equilibrium. This new price is high enough to provide a profit to these new producers but low enough to maintain demand. Just as a receding tide can expose a shipwreck holding treasure, a stable higher price renders many difficult gas-production and -transportation methods worthwhile. How is possible to develop 13,000-ft gas wells on 10-acre spacing? If the target zone is 3,500 ft thick and needs 12 separate fracture treatments, the lack of areal extent is offset by huge vertical extent. But how will the well perform with some zones continuous and others not? Consider the Barnett shale: "The largest gas field in Texas," where the average well is less than 4 years old and water production in the noncore area typically necessitates artificial lift. The Haynesville and Marcellus shales are expected to be equally impressive, even though these tight formations were identified long before drill bits turned to the right. Extensively developed in the US and Australia, coalbed methane still is viewed as "unconventional" in most of the world. For all of you with a 17-year science project waiting for a lucky break, remember that luck happens when opportunity meets preparation, and opportunity is knocking…. Gas Production Technology additional reading available at the SPE eLibrary: www.spe.org IPTC 11307 • "Subsea LNG Transfer System" by William S. Mathews, ExxonMobil, et al. IPTC 11795 • "A Model for Short-Term Supply-Chain Management of an LNG Production System" by Ajay Selot, Massachusetts Institute of Technology, et al. SPE 109182 • "Gas-to-Hydrate Technology, an Alternative Energy for Low-Level Communities in Indonesia" by Adam Nur Bawono, Perusahaan Gas Negara SPE 113816 • "Angsi K-Sand Production Performance: A Case History of Hydraulically Fractured Retrograde-Gas-Condensate Reservoir" by Mohamad Othman, SPE, Petronas, et al.

Technology Focus: Unconventional Recovery (July 2008)

Technology Focus Have you heard the story about the "17-year overnight sensation" (Durham 2005)? (If you work in northern Texas or are involved in unconventional resources, then your answer probably is yes, and if so, please bear with me—it is a great story and worthy of being repeated.) In the early 1980s, in a county on the outskirts of Fort Worth, Texas, there was a privately owned oil and gas company that just would not give up on a novel idea it had for obtaining a new source of gas for a large existing gas-gathering infrastructure and a large gas-processing plant. It seemed that whenever it drilled a well for deeper horizons, it encountered a significant gas show in a very thick shale section that contained methane and some heavier gases. Some brave soul, probably a very young engineer or geologist, suggested testing the shale to see if it possibly could be productive. At the time, the conventional wisdom was that the shale was probably a source rock, but was certainly not reservoir quality and certainly not productive. But the president of the company had faith in his young professionals and gave the go-ahead for testing. The first well, the C.W. Slay No. 1, was an economic failure, as were the next 40 wells (Bowker 2003). It took 17 years for the company to develop an economic technique that worked. How many companies that you know have that kind of patience? In 1999, very few people had heard of the Barnett shale, but by 2001, it was well on the way to becoming the largest gas field in Texas. I think that stories like this make unconventional recovery a very exciting arena in which to work. The resource is there, the demand is definitely there, and it is up to engineers, geologists, and enlightened managers to make it happen. In this issue, we look at three great examples of applying new technology and knowhow in the areas of coalbed methane, tight-gas-field deliquification, and gas hydrates. Is there another 17-year overnight sensation here? You be the judge. References Bowker, K.A. 2003. Recent Developments of the Barnett Shale Play, Fort Worth Basin. West Texas Geological Society Bulletin42 (6): 4–11. Durham, L.S. 2005. The 17-Year Overnight Sensation. Explorer 2005 (May). www.aapg.org/explorer/2005/05may/barnett_shale.cfm. Accessed 5 June 2008. Unconventional Recovery additional reading available at the SPE eLibrary: www.spe.org. SPE 114173 • "Stimulating Unconventional Reservoirs: Maximizing Network Growth While Optimizing Fracture Conductivity" by N.R. Warpinski, SPE, Pinnacle Technologies, et al. SPE 110590 • "Potential for Oil-Shale Development in the US" by Khosrow Biglarbigi, Intek, et al. Additional reading available at OnePetro: www.onepetro.org. OTC 19519 • "Four Critical Needs To Change the Hydrate-Energy Paradigm From Assessment to Production: The 2007 Report to Congress by the US Federal Methane Hydrate Advisory Committee" by Dendy Sloan, SPE, Colorado School of Mines, et al.

Comments: JPT Readers Survey

Every 2 years, JPT takes a close look at how it is doing. SPE members are invited to take a detailed survey on JPT's content, coverage, relevance, strengths, and weaknesses so the staff can gain insight into areas for improvement. In June, an invitation to participate in the 2007 JPT Readers Survey was sent to a random sample of 21,594 SPE members, closely matching SPE members' demographics and job/technical interests. The survey showed an improvement in the overall rating of JPT compared to the most recent survey, which was taken in 2005. Its content was rated favorably (excellent, very good, or good) by 95% of the 2007 survey respondents, with the most frequent response being "very good." This compares to an overall favorable rating of 93% in 2005. A total of 88% of those surveyed consider it to be useful or very useful to them in their jobs, identical to the rating in 2005. The most frequently read features in JPT, in order of frequency, are identical to the 2005 survey: Technology Update, Technology Applications, summaries of technical papers, and Techbits (summaries of technology discussed at SPE meetings). The most favored technical topics among readers, in order of preference, are field development, mature field revitalization, horizontal and complex trajectory wells, high pressure/high temperature wells, well stimulation, multilateral/extended reach, unconventional recovery, reservoir/asset management, IOR/EOR, and tight reservoirs. Among the topics that readers would like to see more information on are offshore processing and gas recovery technologies; health, safety, and the environment; marginal fields; geophysics; sand management; petroleum engineering basics; geomechanics; and CO2 sequestration. The nontechnical topics readers are most interested in reading about are the oil industry's image and reputation, leadership challenges in the industry, career development, employment opportunities, and ethics. Respondents to the survey also assessed what they see as JPT's biggest strengths and weaknesses, and how to improve the publication. JPT's strengths are its up-to-date, relevant information and breadth of coverage; its technical content and focus; its balance between technical content and news/information about the industry and profession; the fact that it is sound technically through its relationship with SPE; and because it is less commercial than other industry trade publications. The publication's weaknesses cited by respondents are that some technical papers deserve more than just a summary; some articles/summaries have dry, slightly academic presentations; and a need for more news about service and operating companies. Representative suggestions for improvement includeAdditional articles with a non-North American focus, and more regional news in generalMore insights on renewable energy and its impact on the future of fossil energyMore contributions and firsthand experiences from readersMore field/asset studiesA "back to the basics" section that revisits basic petroleum engineering and adopted industry practices. Compared to other magazines covering the E&P industry, 72% of the respondents rate JPT better or significantly better than other publications. This percent-age is up from 66% in 2005. Approximately 40% download the online full-length technical papers that have been summarized in JPT.

Overview: Unconventional Recovery (August 2007)

In the year 1419, Filippo Brunelleschi entered a competition to solve the most daunting architectural and engineering challenge of his time: designing and building the Dome of the Cathedral of Florence. The problem was that when the building was designed in the previous century, no one had any idea about how such a dome would be built (imagine that). To further complicate matters, buttresses were forbidden by the city fathers, internal scaffolding was undesirable, and the use of concrete had long been forgotten, which meant the dome had to be built out of bricks. Worse, his rival, Lorenzo Ghiberti, who was appointed coadjutator for the project, publicly mocked his plans and called them unfeasible.* (Think about that the next time you have a bad day at the office!) Fortunately for Florence and for Renaissance architecture, Brunelleschi endured the hardships and technical challenges to design and create one of the world's most famous and admired structures. Today, we are faced with a daunting challenge: How can we supply the world with the energy our economies demand and, at the same time, reduce the emission of greenhouse gases, burn cleaner fuels, and improve air quality in our cities? In this section, we will look at new technologies that hold at least a promise for meeting this challenge: simultaneous coalbed-methane production and CO2 sequestration, gas production from hydrates, and the use of hydrogen as a fuel for automobiles. Certainly, we do not have all of the answers yet, and we will need to rely on innovators, like Brunellschi in the 15th century, to provide ingenious and unprecedented solutions. But with dogged determination, a little patience (it took 16 years to build the dome), and plenty of public education and support, I think we can make a difference that will improve the lives of many generations to come. Imagine that. Unconventional Recovery additional reading available at the SPE eLibrary: www.spe.org SPE 100674 "Data Analysis of Barnett Shale Completions" by B. Grieser, Halliburton, et al. SPE 101109 "Changes in Completion Strategy Unlocks Massive Jurassic Coalbed Methane Resource Base in the Surat Basin, Australia" by R.L. Johnson Jr., SPE, Queensland Gas Company, et al. Available at the OTC Library: www.otcnet.org OTC 19090 "Electrical Collection and Transmission Systems for Offshore Wind Power," by Jim Green, National Renewable Energy Laboratory, et al. * Wikipedia: http://en.wikipedia.org/wiki/Filippo_Brunelleschi and http://en.wikipedia.org/wiki/Florence_Cathedral. Accessed 18 June 2007.

Overview: Unconventional Recovery (August 2006)

I was inspired by a recent broadcast of All Things Considered on Natl. Public Radio and began to think of our industry and what could possibly make a difference in the world—if we, like Bill Gates, had an optimistic belief in technology and management combined with the vast resources of the petroleum industry. Is it possible for us to eliminate some of the top energy-related "diseases"? The production of greenhouse gases certainly would be high on the list, regardless of whether you believe it is responsible for the recent global-warming trend. (Most of us would agree that it is at least a contributing factor.) So, is it "naïve overreaching" to think that we can affect such a gargantuan problem with current or near-future technology? I think we can help. In this issue, the focus is on technologies that hold at least a promise of a solution, either by offering an alternative to dirtier fuels or by eliminating or reducing some greenhouse gases directly. Although expensive to produce and technologically challenging, coalbed methane (CBM) is a clean-burning fuel with tremendous potential for replacing some of the more conventional and "dirtier" resources. CBM is found in nearly every sedimentary basin, and current production is limited only by economics, which is negatively affected by water disposal and low production rates. New advances in recovery methods, such as the use of horizontal production and injection wells, could yield huge increases in CBM production. CO2 storage in deep underground reservoirs is not a new idea, but until recently, very little was known about the storage capacity and viability of such a practice. Recent computer modeling has led to an increased understanding of the trapping mechanisms and suggests optimal injection practices. CO2 sequestration in gas hydrates may offer a viable long-term storage solution while liberating methane gas to use as fuel. Although still in its infancy, this unconventional technology holds tremendous potential for the industry—and the environment. I hope you will enjoy reading these paper highlights; and with an optimistic belief in our technology and management and with our vast resources, I know we can make a difference! Unconventional Recovery additional reading available at the SPE eLibrary: www.spe.org SPE 100021 "A Screening Model for CO2 Flooding and Storage in Gulf Coast Reservoirs Based on Dimensionless Groups" by D.J. Wood, U. of Texas at Austin, et al. SPE 100584 "Evaluation of the Technical and Economic Feasibility of CO2 Sequestration and Enhanced Coalbed-Methane Recovery in Texas Low-Rank Coals" by G.A. Hernandez, SPE, Texas A&M U., et al. SPE 97266 "Depressurization-Induced Gas Production From Class 1 Hydrate Deposits" by G.J. Moridis, SPE, Lawrence Berkeley Natl. Laboratory, et al.

Electrical characteristics of alternative recovery convertors for slip-energy recovery drives

The performance characteristics of four different inverter schemes employed in slip-energy recovery drives have been analysed and compared. The effects of supply impedance upon inverter current and voltage waveforms have been fully accounted for, including the effects of recovery system losses and commutation overlap within the inverter bridges. All three unconventional recovery inverters were found to give markedly better performance than the normal three-phase fully-controlled bridge. In particular, the problems of poor power factor and highly variable reactive power consumption are significantly reduced.