Abstract
Over the last few years, we have successfully treated several production wells across Eagle Ford shale play in South Texas. Shale oils are highly paraffinic with many featuring wide distribution of paraffin molecules that can extend to C100 carbon chains. Consequently, this creates a major risk of organic scale that can deposit in production and flow lines, storage tanks, and process units. With current downturn in global oil & gas market, need for production optimization and for cost reduction urges producers and service companies to work in collaboration and accelerate innovation in chemical treatment strategies. This work is aimed to develop a more in-depth knowledge on how wax formation and gelation of various shale oils are impacted by their chemical composition and production regime and how to select and deploy best chemical additive for ultimate performance during field operation.
We have characterized reservoir hydrocarbons chemistry by common industry practices and studied their wax formation behavior through use of advanced rheology techniques. Measurements of dynamic modulus, gelation point and yield stress at simulated temperature profile that mimic production conditions gave detailed perspective of crude tendency for wax deposition. Information then was plugged into a screening program which includes major classes of polymeric materials and a few selected surfactants. We used a cumulative index to rate performance of various chemistries based on composition of oil samples and actual field conditions.
Viscoelastic properties and gelation behavior of paraffin crystals from ten different crude oils in the Eagle Ford are determined. Despite some compositional differences among the samples, the similarity of their micro and macro physical properties is quite remarkable. Wax formation is highly affected by the presence of high molecular weight paraffin molecules, but gel structure and strength trends were found to be quite complex. We made an attempt to explain the above observations by paraffin fingerprinting. Then we established correlation between structure and performance of chemicals based on targeted paraffinic groups. Identifying key indices for wax control products allowed development of more efficient chemical additives for wax control and mitigation.
To the best of our knowledge, this is the first comprehensive study that presents details of chemical composition, rheological properties, and wax formation characteristics of representative shale oils from Eagle Ford. This study adapted a novel approach by incorporating best field practice data into a product evaluation program and to further improve wax treatment strategies with benefits to shale operators and producers. Viscoelastic models exhibit good potential for accurately capturing the details of wax formation pattern. Lessons learned and proposed approach can be applied in other unconventional developments where wax precipitation and deposition is a major challenge.
