Date(s) - 04/14/2020
11:30 am - 1:00 pm
3D SEISMIC ANALYSIS TO EVALUATE AGI FEASIBILITY OF CARBONATE RESERVOIRS
Authors: Alberto A. Gutierrez, RG ; Jasha Cultreri; Lou Mazzullo, RG
The evaluation of the potential suitability of geologic reservoirs for the permanent disposal of H2S and CO2 requires many of the same methods used in exploration of potential hydrocarbon reservoirs. These tools include traditional geologic methods such as basin, structural, stratigraphic analyses using geophysical logs, production and available well data. The irony of prospecting for acid gas injection (AGI) reservoirs is that while a reservoir with a minimum of penetrations (actual or potential) is most desirable, this condition reduces the data density available to make accurate predictions of reservoir conditions. For these reasons, in areas where reservoirs have not had extensive exploration or penetration, other tools must be used to evaluate the suitability of the potential injection zone. Especially when suitable targets are found at significant depths exceeding 3500 meters, it is critical to reduce the risk of encountering a zone which will not be suitable due to the high cost of drilling and testing wells to these depths.
In the Permian Basin of West Texas and SE New Mexico, good potential AGI reservoirs exist in the Siluro-Devonian and Ordovician section which is comprised of the Devonian, Fusselman and Montoya Formations. These are carbonate reservoirs which were subaerially exposed due to sea level fluctuations resulting in the creation of dissolution features which significantly improve the permeability and porosity of these formations. However, because these events were variable through time and space and the rocks have been subjected to millions of years of structural and hydrothermal alteration, the areas of optimal porosity and permeability have unpredictable and variable boundaries with portions of the formations which have much lower porosity and permeability making them poor AGI candidates. The occurrence of these Karst features and secondary porosity enhancement and dolomitization can be observed in some geophysical logs where they are available but geophysical and geological analysis using seismic data provides an excellent option for evaluating these carbonate reservoirs for AGI potential.
Due to the contrasts in density and corresponding effects on the reflection and refraction of induced seismic waves, these zones show up as anomalously low velocity zones interbedded with other zones of contrasting seismic velocity characteristics. Through the use of multiple vertical slices of 3D data in combination with synthetic seismograms constructed using control wells, the structural and stratigraphic variations which can be used as surrogates for improved porosity and permeability can be mapped in strategic directions within the study areas. In addition, the use of time slices of the 3D seismic data allow for the evaluation of the areal extent of reservoir zones of various potential feasibility for AGI. These analyses will significantly reduce drilling risks and potential economic impacts of drilling a well in a zone which will not provide sufficient permeability to allow injection of treated acid gas (TAG) at desired rates within acceptable and permit-controlled maximum surface injection pressures (MAOP). In addition, the evaluation and better mapping of porosity within a potential AGI reservoir unit will allow for the more accurate prediction of the total capacity of the reservoir.
This paper presents a brief review of the technology, logistics and costs of obtaining 3D seismic data and a detailed examination of its utility in the evaluation of carbonate reservoirs for AGI. The actual use of 3D seismic to evaluate potential AGI reservoirs is evaluated through the examination of two case studies from the Permian Basin where Silurian-Ordovician carbonate reservoirs were evaluated using this tool. One area was evaluated using available seismic data which was provided by an adjacent operator and the second area was evaluated after conducting an 18 square mile survey designed by Geolex, Inc. and shot by Dawson Geophysical. The first of the two locations was tested very successfully with an AGI having been completed in January 2017 which has been operating continuously since that time averaging about 142,000 m3/day (5,000,000 ft3/day) of TAG injected at an average pressure of 10.34 MPa (1500 psig). The second area was tested by a well in 2018. It is now taking about 17,000 bpd at 130 psig surface pressure.
Sophisticated and costly tools such as 3D seismic in order to find the best potential deep AGI targets are being used increasingly in response to the need to develop AGI disposal zones which will serve the needs of increasing sour gas production in the Permian Basin. This is due to the extensive development of zones that are productive of hydrocarbons and the need to go to increasingly deeper and more expensive targets in areas of limited well penetrations of potential AGI reservoirs
Mr. Alberto A. Gutiérrez has over 42 years of experience in the fields of petroleum geology, hydrogeology and environmental geology. He is a registered professional geologist in twenty states in the USA and with AAPG and AIPG. Mr. Gutiérrez has served as the principal-in-charge and lead geologist on feasibility studies, permitting, drilling, completion and commissioning of over 20 acid gas injection (AGI) projects in the Permian and San Juan Basins. His company (Geolex, Inc.) is currently conducting numerous additional turnkey AGI projects both domestically and abroad. In addition to his work in the oil and gas sector, Mr. Gutierrez has done extensive work on the fate and transport of contaminants in various environmental media. In 1982, after working for several years as a program manager for an environmental consulting firm, Mr. Gutiérrez founded Geoscience Consultants, Ltd. in 1983. By 1992, it had revenues of over $40 million and 450 employees. From its inception to 1994, when the business was sold, Mr. Gutiérrez operated the company as President and CEO. After selling the company to BDM, Inc. he was part of the management team that took the company public and later sold it to Northrup Grumman. In 1996, he founded Geolex, Inc and remains its president and CEO. Geolex is a specialized and highly-respected international geologic and reservoir engineering consulting firm providing turnkey AGI services, environmental litigation support, liability assessment, merger and acquisition, due diligence and strategic environmental services.
Mr. Lou Mazzullo has 44 years of experience in resource exploration and development in the fields of strategic minerals, uranium, and oil and gas, and in environmental geology (groundwater assessment and remediation, oilfield spill mitigation, petroleum facilities audits). He is a registered professional geologist in two states, and a Certified Petroleum Geologist with the American Association of Petroleum Geologists (AAPG). He has been a successful Petroleum Geological Consultant for over 32 years, and briefly served as Chief Geologist for Nearburg Producing Company in Midland, and Senior Geologist for Ameristate Exploration and Brigham Oil Company in Austin. Mazzullo has been very active in oil and gas exploration and development in the Permian Basin, where he resided for 12 years, and experienced in most western and midwestern petroleum basins, and some overseas basins. ). He has also assisted Geolex, Inc. on feasibility studies, permitting, drilling and completion of many acid gas injection and CO2 sequestration wells in numerous domestic basins over the past 15 years. He is the author of numerous papers and talks on the petroleum and uranium geology of the Permian, Williston, and San Juan Basins, and the recipient of two AI Levorsen Best Paper Awards (AAPG), the Cheney Science Award in 2005 (Southwest Section AAPG), and other speaking awards in the field of Petroleum Geology. Mazzullo is the past-president (1999-2000) of the Rocky Mountain Section AAPG and the Permian Basin Section SEPM (1988-89). He is currently a semi-retired Geologic Advisor based in Denver.