Life Beyond 80: A Look at Conventional WAG Recovery Beyond 80% HCPV Injected in CO2 Tertiary Floods

David H. Merchant
2010 SPE International Conference on CO2 Capture, Storage, and Utilization   unpublished
During the past 38 years, CO 2 flood technology for Enhanced Oil Recovery projects evolved from a partially understood process filled with uncertainties to a process based on proven technology and experience. Many questions involved with CO 2 flooding have been thoroughly analyzed and answered. This knowledge is currently being used by a limited number of companies that actually know how to design, implement, and manage a CO 2 flood for long term profit. Unfortunately, this knowledge has not
more » ... nowledge has not been disseminated to operating companies interested in EOR flooding or to CO 2 Sequestration Communities interested in storing CO 2 in EOR projects. The primary objective of this report is to target "Conventional WAG Techniques" which have been used in over 90% of all the Enhanced Oil Recovery projects implemented in the Permian Basin in Texas, Colorado, Oklahoma, and Wyoming. Over the years, oil companies have reported a wide range of values of Tertiary Oil Recovery, CO 2 Utilization, and CO 2 Retention, resulting in a wide range of variation and uncertainty. Many of the numbers reported to date are tied to a specific HCPV CO 2 Injected based on some Economic Cut-off. This typically has been in the range of 30% to 80% HCPV Injected. The question becomes "What is life after 80% HCPV?" And "What effect does life after 80% HCPV have on Tertiary Oil Recovery, CO 2 Utilization and CO 2 Retention in different producing formations?" Results of this study show Tertiary Oil Recovery can be as high as 26% OOIP when slug sizes exceed 190% HCPV injected. Carbon Sequestration Options: Five Recovery Methods for Enhanced Oil Recovery (EOR) Most Enhanced Oil Recovery Projects use one of the following five operating methods: Conventional WAG Recovery, Gravitystabilized Recovery, Double Displacement, Gas-cycling or Huff-and-Puff. The primary difference between methods depends on the reservoir geology and well pattern configuration. In Conventional CO 2 floods, typical of West Texas, the formations are basically flat (Ramp Sequence), low perm, the fields are developed on pattern spacing (e.g. 5-spot patterns, 9-spot patterns, or Chickenwire patterns), and Conventional WAG Operating schemes are used to control mobility and CO 2 flood response. In conventional WAG operations, the objective is to minimize the amount of CO 2 purchased (CO 2 stored in Sequestration projects), which is typically in the range of range of 30%-40% of the total HCPV CO 2 injected. In un-conventional Gravity-Stabilized and Double Displacement case histories, Flue Gas, CO 2 , Lean Gas or N 2 is usually injected in the top of the structure and oil is produced from the bottom. More CO 2 can be sequestered than conventional WAG operations. As much as 80% of the total pore volume can be displaced with CO 2 . However, the reservoir must meet certain fluid-dynamic criteria and have structure to make the gravity-stabilized process work. In Gas-cycling projects, typical of projects operated by Denbury in Mississippi, CO 2 is cycled through the formation. As much as 6 pore-volumes of CO 2 are injected to recover 18% OOIP. In Huff-and-Puff operations, the CO 2 is injected into and produced from the same well. The objective is to mobilize tertiary oil in the near vicinity of the well-bore, and then produce the CO 2 and tertiary oil back. Then repeat the process (typically with 3 cycles). The process technically works. The economic success or failure depends on many factors. The amount of CO 2 sequestered is minimal when compared to the other recovery methods. Conventional WAG Recovery Conventional WAG Operating Methods in the Permian Basin fall into one of four categories: 1. Continuous CO 2 Injection 2. Constant WAG Injection 3. Tapered WAG Injection 4. Simultaneous CO 2 Injection (Limited use)
doi:10.2118/139516-ms fatcat:xqes5le3k5denpztdhb4g77oai