The first three articles in this series have discussed problem identification, problem understanding; solution design, execution, and performance; and benefit analysis and economic analysis. We have discussed methods and techniques that should help in our efforts to improve the solution success rate, but we still have further improvements to make.
Part 4 provides an overview of ongoing research and recent technology improvements focused on improving sweep efficiency or conformance solutions taking place in both academia and the service industry within the US. This article does not review efforts taking place inside oil production companies or national oil companies as that work is generally not publicized until completed.
Before we start this review, let’s capture some thoughts that were expressed by several department chairs and other leaders in the industry. There is a common feeling that the level of research activity on all conventional oilfield recovery problems has suffered from a change in interest and funding over the past 10 to 15 years.
Research on conformance or sweep efficiency problems is a subset of conventional oilfield recovery issues and thus has also suffered from this reduced interest. Instead, a significant rise of unconventional oilfield recovery needs and focus on greenhouse gases (GHG), carbon footprint, and the energy industry transition has shifted the priorities at many universities, governments, and service providers. This shift in efforts has resulted in a significant redistribution of resources that were once focused on conventional oilfield recovery issues.
The number and types of conventional oilfield recovery problems has not changed; if anything, they continue to grow, but the addition of unconventional resources and their unique character, along with the push for studies on GHG, carbon footprint, and energy transition without a corresponding increase in funding and manpower has diluted our ability to respond as an industry to these needs.
This perspective is offered as a simple observation of conditions that exist in the energy research arena. No judgment is made on the appropriateness of this change or the overall situation. Simply be aware that as an industry we have many challenges to face in the future and some will suffer as others are prioritized.
As a result of this and some other reasons, several universities such as Colorado School of Mines, Louisiana State University, Penn State, Stanford University, University of Houston, University of Southern California, The University of Tulsa, and University of Wyoming are not reporting any active or current efforts on conventional asset sweep efficiency or conformance solution research. This does not mean that all interest in these technologies has been lost, only that no current research activities are underway. This is unfortunate, but I believe it is representative of this industry shift.
Now, back to the primary focus of this article.
Outline of Research Efforts on Conformance or Sweep Efficiency Solutions
To provide organization and focus on the research efforts taking place, this review divides the types of research into two major categories: 1) research on physical intervention methods, tools, and techniques; and 2) computational methods to generate improved sweep efficiency of fluids and provide economic efficiencies.
We have not included an area where these two categories overlap: those computational methods that focus on how to predict physical intervention solutions. This numerical modeling practice has been taking place for many years and although very valuable and still filled with problems, those efforts are not covered.
Research on Computational Methods
Only research or sweep enhancement efforts are included which use some form of computational method (such as capacitance resistance model (CRM), streamline numerical simulation method, finite element modeling, wavelet analysis, and artificial intelligence, etc.) to generate recommendations for pattern reconfiguration, fluid rebalancing, or modified well placement to improve sweep efficiency or conformance control. Except for modified well placement, these results only require a limited amount of intervention by the operator.
The University of Texas at Austin. In the area of computational research methods, Larry Lake, professor, Shahid and Sharon Ullah Endowed Chair in Petroleum and Geosystems Engineering, continues to enhance the application of CRM technology to the process of fluid rebalancing to improve sweep efficiency. His efforts are intended to enhance and extend this technology and its application to pattern and fluid rebalancing that is designed to improve conformance or sweep efficiency within the reservoir.
Texas A&M. Akhil Datta-Gupta, professor of petroleum engineering, has been conducting research on improving sweep efficiency through optimal rate control in waterflooding and CO2 injection using constrained optimization and machine learning algorithms. The goal is to facilitate rapid decision-making while accounting for well- and field-level rate and pressure constraints and underlying geologic uncertainty. The use of streamlines and time-of-flight concepts are the core technologies in this research.
Research on Physical Intervention Methods, Tools, and Techniques
This section reviews technical improvements that require a physical intervention into the wellbore or reservoir. They require equipment, manpower, and materials to implement the physical changes.
Colorado School of Mines. Luis Zerpa, Harry D. Campbell Endowed Chair in Petroleum Engineering, recently completed work on HPHT (high pressure/high temperature) stable foams for mobility control in steam displacement floods. This effort centered on an HPHT apparatus which allowed visual inspection of the foam to establish its stability. No further work is planned.
Louisiana State University. Andrzej Wojtanowicz, Texaco-Endowed Environmental Chair in the Craft and Hawkins Department of Petroleum Engineering, guided the conformance technology R&D program of downhole water sink (DWS) for many years. Upon his retirement, the consortium has become inactive, but the material and application of technology remains available at LSU. DWS technology has been implemented worldwide in a variety of configurations and applications including well stimulation, water coning control, recovery enhancement, reservoir pressure maintenance, and produced water cleanup and water volume reduction.
Although DWS does not directly influence sweep efficiency, it supports and prolongs bottomwater drive which allows extended operations and overall improved recovery. DWS’s ability to control water coning has recently expanded to production of heavy oil with bottomwater and to increase oil rate with reduced water cut in a multilayer reservoir. Improved oil recovery potential from a gas-capped strong-waterdrive reservoir by including DWS in horizontal wells in gas-assisted gravity drainage production systems is also being currently applied in the Middle East. This technique has been dubbed gas and DWS-assisted gravity drainage, or G&DWS-AGD. Again, although current research on this technology is not taking place, LSU continues to support exchange of knowledge and application of this technology.
Missouri University of Science and Technology. Baojun Bai, Lester R. Birbeck Endowed Chair in Petroleum Engineering, and Thomas Schuman, associate professor of chemistry, and Missouri S&T have pioneered the technology of conformance control using preformed particle gels (PPGs) which have been applied in more than 10,000 wells in mature oil fields.
Missouri S&T’s recent research on conformance has focused on solving void space conduit problems, whether they are fractures, wormholes, or features that have been enhanced by rock dissolution or sand production. In the past 8 years they have synthesized and patented eight products and have worked with joint industry project members to provide commercially available products.
These products are PPGs, which not only have swelling properties, but once swollen and in place, the grains bond together into a cohesive mass which limits any further movement. This product is called reassembling preformed particle gel. These products can meet the requirements of reservoirs with high-temperature (175°C) and high-salinity conditions. This work has included the synthesis, property testing (swell rate, bond rate, strength, etc.) at a variety of conditions (temperature and water chemistry) and physical model testing to evaluate transport. Some recent efforts have shifted to designing and evaluating small submicron particles for plugging in permeable rock.
New Mexico Tech and University of Bergen. Bergit Brattekås, researcher at University of Bergen, and Randall Seright, adjunct faculty, Petroleum Recovery Research Center, New Mexico Tech, continue to focus their research on fundamental flow dynamics of polymer gels in both fractures and matrix permeability. Recent efforts have shifted from the influences of water to the influence of CO2 on the gels, not only for CO2 flooding but also for CO2 sequestration. In addition, Brattekås has been doing work on the application of gels with foam systems for CO2 mobility and conformance control.
List of contact points by research and new technology discussed in this article, as of 18 September 2023.
The University of Oklahoma. Ben Shiau, Mewbourne Chair, professor at Mewbourne School of Petroleum and Geological Engineering, is leading research focused on developing a modified matrix acid stimulation formula aimed at selectively generating deep-penetrating wormholes into the rock surrounding the wellbore without reducing mechanical integrity. This research also targets avoiding excessive stimulation that can result in conformance problems. His second research effort focuses on utilizing an oil-induced viscoelastic emulsion with surfactant fluids to control mobility and reservoir permeability variance to attain a better overall sweep efficiency of the process.
The University of Texas at Austin. A variety of efforts are taking place at UT-Austin that target physical intervention methods to solve conformance or sweep efficiency problems. Quoc Nguyen, J.H. Centennial Professorship, Hildebrand Department of Petroleum and Geosystems Engineering, is working with both aqueous and nonaqueous foams for mobility control and better distribution of injectants in high-permeability-variance reservoirs and using foams for gas shutoff in both vertical and horizontal producers. He is also working with nanoparticles designed for high-temperature stability in conformance control of high-perm intervals. Ryosuke Okuno, associate professor, Pioneer Corporation Faculty Fellow in Petroleum Engineering and Energi Simulation Industrial Research Chair on Carbon Utilization and Storage, is working with aqueous formate solution as a viscosifier and CO2 nanobubble carrier to influence both mobility ratio and improve distribution of CO2 contact within oil-bearing zones. Matthew Balhoff, department chair and professor, Hildebrand Department of Petroleum and Geosystems Engineering, is working with delayed silica gels for both plugging of caprock in CO2 storage and potential use in high-permeability control for conformance problems. In addition, he is studying the effects of viscoelastic polymers and viscous surfactant microemulsions in tight fracture displacement, designed to improve sweep efficiency. Kishore Mohanty, W.A. (Monty) Moncrief Centennial Endowed Chair in Petroleum Engineering, Hildebrand Department of Petroleum and Geosystems Engineering, is working on foams with surfactants and nanoparticles targeted for high-salinity, high-temperature reservoirs, and fractured shales. These foams can also be designed to impart wettability alteration properties to improve displacement efficiency. He also works on preformed particle gels which swell at increasing salinity for conformance control.
Service Company Review
The following service companies have all shown an aggressive approach to solving conformance and sweep efficiency problems. This section highlights only new or recently introduced products (past 5 to 7 years) that are focused on solving conformance or sweep efficiency problems, as provided by the companies.
Halliburton. Halliburton is developing proprietary research on new technologies related to naturally fractured reservoirs and horizontal completions. Recently, the company launched four products that add to its existing solutions, targeting conformance or sweep efficiency issues. Thermatek and EquiSeal fluid treatment services were both designed to improve the ability to control fluid movement in horizontal or high-angle wellbores. Both products use thixotropic properties to deter product movement from gravity segregation or slumping. They also deter crossflow displacement between the time of pumping and the product’s final transformation into a rigid or stronger product capable of resisting larger differential pressure.
The company also improved its relative permeability modifier (RPM) product, WaterWeb treatment service, to be more effective in carbonate reservoirs. Most RPMs are designed for control in sandstone reservoirs only, but Halliburton stated it has enhanced the product’s functionality in carbonate reservoirs.
Finally, the service provider has focused a significant amount of attention on an important aspect of product placement control. Its new SPECTRUM e-IP electric inflatable packer service allows for more efficient control of product placement either through a dual-element straddle design or a single-element squeeze design.
SLB. SLB recently developed AllSeal. The system comprises a single nanoparticulate additive and is designed to shut off formations greater than 50 md and up to several darcies. The nanoparticulate system works by physical pore plugging and does not rely on a curing mechanism. It is suitable for all connate water salinity environments and can withstand temperatures up to 350°F. The system can be tuned depending on the formation permeability, is easy to prepare at the wellsite, and does not require gelation time. Laboratory core experiments showed that most of the matrix plugging occurs in the first 2 to 6 in. of the core; thus, reperforating beyond the damaged matrix is possible. This feature was confirmed in the field when oil layers were successfully reperforated after all perforations had been shut off.
The OneSTEP EF efficient, low-risk sandstone stimulation solution and OpenPath Reach extended-contact stimulation service are additional products designed to acid stimulate sandstone and carbonate reservoirs. These acid systems—when designed with Kinetix Matrix stimulation design software, which integrates reservoir petrophysical and treatment fluid chemical data, and deployed with the ACTive Matrix CT real-time stimulation service, which utilizes distributed temperature sensing data to provide real-time downhole measurements—combine to improve targeted stimulation and ultimately improve sweep efficiency.
Baker Hughes. During the past 3 years, every Baker Hughes inflow control device (ICD) designed for conventional applications has been upgraded or validated for water or gas injection. Baker Hughes Equalizers’ performance is tested in injection mode, and a minimum differential pressure rating of 2,000 psi across the restrictor has been implemented to comply with most of the injection wells requirements. Every Baker Hughes ICD design is integrated with sliding sleeves as an option to optimize the configuration of the completion once the injection well’s operation data is analyzed. The Equalizer Orifice Injection Valve was introduced in 2021 to eliminate crossflow in fluid-injection wells and water hammer in water-injection wells.
AquaCUT Plus RPM is the latest subsurface water conformance technology from Baker Hughes that decreases the water cut in both sandstone and carbonate wells, reducing associated processing and disposal costs of produced water while also extending the productive life of the well.
PQ Corporation. PQ is one of the top suppliers of sodium silicate to the oil industry. Since the introduction of silicate-based conformance treatments in the 1920s, the chemical structure of sodium silicate has remained relatively unchanged. A new production method now allows for a silicate with significantly less sodium called S45. This lower-alkaline silicate requires only half the usual quantity of setting agent and allows for longer and more controlled set times. The resultant solidified silicate has improved strength and better dimensional stability. Another area of research is in the development of expansive products. Many (but not all) cements, polymers, and sodium-silicate systems are susceptible to a small volume reduction following placement and setting. In the case of silicate-based sealants, the issue of potential shrinkage has been effectively addressed through the incorporation of gas-generation additives. Metals like zinc or aluminum can be formulated to generate gas over a few seconds to several hours. The expansion in volume can span from a minor increment to a substantial enlargement.
Worldwide Efforts. Due to the limited space for this article, the focus was specifically on US universities and major service providers and one product supplier actively working on conformance solutions. However, it is important to note that there are a variety of universities in Canada, China, Colombia, England, France, Germany, India, the Middle East, Mexico, and Norway, and maybe some others, that could have efforts focused on solving sweep efficiency or conformance problems. In addition, some other service companies and suppliers such as Kemira, Poweltec, and SNF were not reviewed even though they each have focused efforts on conformance and sweep efficiency improvement.
Bottom line: Significant efforts are still taking place in the US and around the world. It is not to the same extent as in the past, and although we have experienced a significant shift in effort and funding, problems in sweep efficiency and conformance still exist and some important efforts remain.
David Smith, SPE, is currently the president and principal advisor for Oilfield Conformance Consulting LLC and an adjunct professor for Missouri University of Science and Technology (MS&T). Prior to his current efforts and for approximately 20 years, Smith was the global conformance engineering advisor for either ConocoPhillips or Occidental Petroleum. Prior to that he was a project manager in conformance water management for Halliburton and held several positions within ARCO that were associated with profile modification and sweep improvement. Smith has been an active SPE member for more than 45 years. He was the technical program chairman for the 2014 SPE EOR/IOR Conference in Tulsa, a past co-chairman of the SPE EOR/IOR TIG (Technical Interest Group), and an SPE Distinguished Lecturer in 2019–2020. Smith holds a bachelor’s degree in geology from Pacific Lutheran University and an MS in petroleum engineering from Stanford University.
