Aproject being undertaken by The Letton-Hall Group, Impact Technologies LLC, and Clean Tech Innovations LLC (CTI), with funding from the National Energy Technology Laboratory, will demonstrate the ease of use and potential of carbon dioxide (CO) injection/production profile modifications using silica polymer initiator (SPI)- COgel systems. The objective is to advance SPI-COEOR gel technology by performing multiple small-scale field injectivity tests using both "huff and puff" and conventional pattern flood applications. A secondary objective of the project is to improve the SPI- COgel integrity by testing a super-absorbent polymer instead of the polyacrylamide currently being used.
Issues associated with using COfor EOR are its low density and viscosity compared to the crude oil and brine in the reservoir. The injected COhas substantially higher mobility relative to the crude oil and brine, which promotes fingering and early breakthrough of the COto the production wells. High conformance or sweep efficiency (i.e., good contact with all the crude oil in the reservoir) is particularly critical in costlier COfloods where the end result of poor sweep efficiency is less oil recovered with substantially higher costs resulting from multiple handling (production, compression, and reinjection) of the CO.
Research has gone into developing gels for the primary COphase, but none are low-cost and commercial. A new SPI gel system may aid in the conformance problem with COfloods. Of particular importance to this and other COinjection projects is the use of an external initiator such as CO. In SPI-COgels, the CObecomes the external initiator of the SPI fluid following its placement in the reservoir.
An SPI mix slug will be incorporated in the water cycle of a water-alternating-gas injection, and the COslug that follows will finger through and permeate the more viscous aqueous SPI mixture in the flow path, generating carbonic acid, which will immediately initiate the gelation process. This newly set SPI gel diverts the COthat follows and causes it to finger and dissolve into fresh SPI mix, leading to SPI gel formation at additional locales. The process continues until the COis fully blocked or all the SPI mix is consumed.
The SPI gel can improve sweep efficiency to a greater degree than conventional systems because it sets up in the high-permeability paths that the COhad traveled previously and is unique in that it is silicate-based and will remain a low-viscosity fluid until gel initiation is triggered by CO. This is a clear improvement over current technology where the gel gradually sets up as a function of time, regardless of location. In addition, the final product in commercial quantities is expected to be less expensive than competing polymer gels or other systems.
US COEOR production has grown by 4%/year over the last 20 years to today's level of 280,000 b/d. The use of SPI gels is anticipated to further improve those levels by 1%/year within a few years of a successful demonstration and up to 3%/year in future years. SPI could add more than 300 MMbbl of otherwise bypassed reserves over 10 years.
Accomplishments
The team has been in contact with major COflood operators to ascertain their needs and to inquire about performing tests in their fields. Several industry contacts have indicated that SPI gels have a place in the COmarket if the gels perform as expected during the project's field test. Legal agreements are being pursued with two companies, and one company has provided the project team with field data, fluids, and core segments for use and analysis. One major COflood operator wants to get to the field right away, while other operating companies have expressed interest.
The CTI laboratory in Bartlesville, Okla., performed more than 600 gel forming bench tests, half at 23°C (74°F) and half at 60°C (140°F). Approximately 40 additives have been evaluated to date at various concentrations and combinations with additional additives. Three formulations look very promising as candidates for further sand pack testing.
The base SPI polyacrylamide polymer was changed to a ultra-high molecular weight polymer that is much easier to hydrolyze. This has benefits of easier mixing in the field and better isolation of the SPI mix within high-permeability zones, a key interest of the industry.
A full CO-capable sand pack system was developed at the CTI lab. Operational improvements to the modified sand pack system have been completed, allowing the use of supercritical COat 1,500 psi. These improvements include:
- Safe handling and discharging of CO;
- Accurate means to meter and deliver supercritical COto core apparatus for sand pack testing; and
- Accurate means to meter and account for all gas and liquid mass exiting the system and other improvements to aid in closing a mass balance (a 2% mass balance closure is anticipated).
Impact Technologies is continuing to communicate with chemical providers and COoperators on a frequent basis with the goal of securing multiple COflood operators for field-testing of the SPI gel. The company will begin to order the required chemicals necessary to complete testing and begin treatments in selected fields.
Test plans for field activity will be developed and will include preparation of the well and site for the field injectivity test (i.e., roads to the well site must be accessible); available access to electricity unless generation is anticipated and desired; finalization of legal documents (liability releases, safety training, data releases) before moving onto the site; obtaining injection well and offset well data oil rates, water rates, COrates, pressures, profile surveys, tracer surveys) to establish a pre-test baseline; and ordering and delivery of pumps, rate/pressure recording, and metering equipment to the field site.
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