Energy Policy Act of 2005 (Ultra-deepwater and Unconventional Resources Program)
Preformed Particle Gel for Conformance Control
This project seeks to establish methods to optimize particle gel treatments for increasing oil recovery and reducing water production by improving the efficiency of water flood sweep.
Missouri University of Science and Technology (Formerly University of Missouri – Rolla, Rolla, MO 65409-1330)
ChemEOR Company, Corvina, CA 91723
BJ Services, Tomball, TX 77375
Excess water production is a major issue that leads to early well abandonment and unrecoverable hydrocarbon for wells in mature fields. Gel treatments at water injection wells are used to preferentially plug off the water thief zones, and are a proven, cost-effective method for improving sweep efficiency in reservoirs and reducing excess water production. A newer trend in gel treatments is the use of preformed particle gels (PPG) to overcome some of the distinct drawbacks inherent in in-situ gelation systems.
In-situ gelation systems have been widely used to control reservoir conformance. The mixture of polymer and “gelant” (a crosslinker) are injected into the target formation and react to form a gel to fully or partially seal off the formation at reservoir temperature with gelation occurring at reservoir conditions. In contrast, with a preformed gel the gelation occurs at the surface, with the gel injected into the reservoir. No gelation occurs in the reservoir.
The drawbacks of using in-situ gel systems are lack of gelation time control and the uncertainness of gelling quality due to shear degradation, chromatographic fractionation or a change in gelant composition due to the dilution of the mixture by formation water. PPGs address these drawbacks through synthesis prior to formation contact. PPGs are strength and size-controlled, environmentally friendly and are stable in the presence of most reservoir minerals and formation water salinity. The process is also simpler, with the handling of only one component during the injection process.
Treatments with PPG could be an effective choice if:
- faults or fractures cross a deviated or horizontal well;
- single fractures cause channeling between wells;
- natural fracture systems allow channeling between wells;
- super K channels for mature waterflooded oilfields
In this project, researchers will study gel particle transport through fractures and fracture-like channels. The ultimate purpose of the project is to establish methods to optimize particle gel treatments to increase oil recovery while reducing water production, by improving water flood sweep efficiency.
ChemEOR is a provider of chemical solutions for improved well performance and enhanced oil recovery processes. For this project, ChemEOR will provide a series of customized PPG products needed to conduct the laboratory tests necessary to evaluate PPGs as selective plugging agents. The variety of results may be interpreted to aid in the field design of PPG treatments for a large range of formation conditions.
BJ Services is a provider of oil and gas well production services. For this project, BJ Services will deploy the results found in the laboratory to the field and provide expert guidance to ensure field data analysis supports the laboratory program. BJ Services will also generate the data necessary for faster deployment of this new technology for use by small producers.
Deliverables for this project will include a series of reports on the tasks as they are completed and a final report integrating the results of the project.
This project will provide data about where particle gels can best be used; fundamentally an improvement in knowledge and will also provide new methods to enhance gel treatment efficiency. The primary benefit from this project could be the subsequent deployment of optimized PPG technology in the U.S., increasing the ultimate recovery from mature oil and gas fields by increasing income and reducing operating costs, as well as reducing water production rates and the associated environmental risk and impact of any saltwater spills.
An estimate of actual impacts will require an estimate of the level of post-research PPG technology deployment in the U.S., the wells/fields where the technology can be applied and the potential for incremental oil/gas production resulting from its application in those fields.
The field applications of preformed particle gel (PPG) treatments for conformance control in various reservoir conditions were summarized and analyzed, which will provide guidance where PPG can be used. The reservoirs that PPG has been applied to include high temperature, high salinity, thick heterogeneous zones with crossflow, severe sand production, polymer flooding and CO2 flooding.
A spreadsheet was designed and it covers the required Data for PPG treatment design and was posted in the website http://web.mst.edu/~baib/PPG.htm [external site] for small producer download.
Screen models were constructed to test the strength of the swollen particle gel and study the effect of injection rate on the injectivity of particle gel. Experiential results from screen model tests indicate the particle injectivity mainly depends on the swelling capacity and the open-hole size of a screen. Increasing particle sizes and injection rates cannot significantly increase the injection pressure. This is in a good agreement with the real-time injection pressure and injection rate change which were observed during practical particle gel treatments. These gel particle injection behaviors are completely different from conventional particles in that they are elastic and deformable during extrusion.
Transparent fracture models were constructed to visually track swollen preformed particle gel (PPG) propagation through open fractures and water flow through PPG placed in fractures. It was observed that PPG propagated like a piston along a fracture during PPG injection and a gel pack was formed in the fracture after gel placement and water broke through the particle gel pack to create several water channels to discharge water from the outlet during water injection after PPG placement. The factors that influence PPG injectivity and plugging efficiency have been investigated. Results show that PPG injectivity increases with fracture width and flow rate and decreases with brine concentration on which PPG swollen ratio is dependent. PPG can reduce the permeability of different width fracture to the same level. Full factorial experimental design was performed to rank the influence of injection rate, fracture width, and PPG swelling ratio on the response of pressure, resistance factor and injectivity.
The compatibility of particle gels and surfactants was evaluated. The objective of this research is to test if the combined technology of PPG treatments and surfactant injection can significantly improve the gel particle treatment efficiency and thus improve overall oil recovery. Results show (1) surfactants have negligible effect on PPG swelling ratio; (2) Equilibrium surfactant concentration in excess brine increases after swelling of gel particles; (3) Gel strength in terms of dynamic modulus G’ (storage modulus) and G” (loss modulus) can be reduced to a much lower value. But the gel strength can be recovered after the surfactants have been removed. Moreover, a new technology of forced surfactant imbibition can be developed by combination of particle gel and surfactant. The new technology will greatly benefit the oil industry by improving oil recovery while reducing water production.
Preliminary results about particle gel damage on unswept zones and areas show that PPG will not form low permeable gel cake on the surface of low permeability rock, which might explain why PPG treatments in field applications rarely have had negligible effect on oil production.
SPE 129908 “Preformed Particle Gel Transport through Open Fractures and its Effect on Water Flow,” by Hao Zhang and Baojun Bai was presented at the 2010 SPE Improved Oil Recovery Symposium held in Tulsa, Oklahoma, USA, 24–28 April 2010. This paper described the project’s transparent fracture models and the results that showed that PPG injectivity increases with fracture width and flow rate and decreases with brine concentration, on which PPG swollen ratio is dependent.
A paper submitted to Industrial & Engineering Chemistry Research titled “Using Screening Test Results to Predict the Effective Viscosity of Swollen Superabsorbent Polymer Particles Extrusion through an Open Fracture” was accepted for publication. An abstract has been submitted for the SPE EOR Meeting in Malaysia in July 2011.
The project has been completed. The final report is available below under "Additional Information".
Project Start: Oct 1, 2008
Project End: Sept 30, 2010
DOE Contribution: $520,212
Performer Contribution: $266,504 (including $130,000 from BJ Services and $25,000 from ChemEOR Company)
RPSEA – Martha Cather (email@example.com or 575-835-5685)
NETL – Chandra Nautiyal (Chandra.Nautiyal@netl.doe.gov or 281-494-2488)
Missouri University of Science and Technology – Baojun Bai (firstname.lastname@example.org)
Final Project Report [PDF-6.07MB]
Annual Report October 2008 – Oct 2009 [PDF-2.70MB]
Preformed Particle Gel Transport Through Open Fractures and its Effect on Water Flow [PDF-580KB] - SPE 129908
Semi-Annual Report October, 2008 - March, 2009 [PDF]