Life Beyond 80 - A Look at Conventional Wag Recovery Beyond 80% HCPV Injection in CO2 Tertiary Floods

Abstract

During the past 38 years, CO2 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 CO2 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 CO2 flood for long term profit. Unfortunately, this knowledge has not been disseminated to operating companies interested in EOR flooding or to CO2 Sequestration Communities interested in storing CO2 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, CO2 Utilization, and CO2 Retention, resulting in a wide range of variation and uncertainty. Many of the numbers reported to date are tied to a specific HCPV CO2 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, CO2 Utilization and CO2 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 CO2 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 CO2 flood response. In conventional WAG operations, the objective is to minimize the amount of CO2 purchased (CO2 stored in Sequestration projects), which is typically in the range of range of 30%-40% of the total HCPV CO2 injected. In un-conventional Gravity-Stabilized and Double Displacement case histories, Flue Gas, CO2, Lean Gas or N2 is usually injected in the top of the structure and oil is produced from the bottom. More CO2 can be sequestered than conventional WAG operations. As much as 80% of the total pore volume can be displaced with CO2. 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, CO2 is cycled through the formation. As much as 6 pore-volumes of CO2 are injected to recover 18% OOIP. In Huff-and-Puff operations, the CO2 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 CO2 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 CO2 sequestered is minimal when compared to the other recovery methods. Conventional WAG Recovery