Iron sulfide scale can be relatively common-place in maturing oil wells and produced water handling systems. Iron sulfide can also be commonly formed as a corrosion product, due to sour corrosion resulting from H2S containing fluids being processed through carbon steel tubulars. As more sour production is brought on-stream iron sulfide continues to become more prevalent. There are few options for removing deposits of iron sulfide scales especially when it comes to choice of chemistry. This paper discusses the most commonly performed techniques for iron sulfide removal, including hydrochloric acid, organic acids and THPS, and the varying degrees of success that these chemistries have in application. Challenges using hydrochloric acid are encountered due to the potentially high yield of H2S upon dissolution of the scale, along with FeCl2 and therefore the potential of secondary deposition. This paper provides data on the development of a new dissolver for iron sulfide. Dissolver tests were performed initially on laboratory generated iron sulfide scale to optimize the formulation. Further testing was performed on different polymorphs of iron sulfide including pyrite, pyrrhotite, troilite, marcasite and mackinawite. Furthermore, several field scales were obtained and after XRD analysis, tested with the novel dissolver chemistry. It was shown that the new chemistry significantly outperformed THPS based dissolvers (active for active) and as well as 7.5% HCl. The corrosion rate of the novel chemistry was significantly lower than inhibited HCl and commercial THPS based blends. Testing was also performed at high pressure in order to understand the influence that pressure has on dissolution rates for all the commonly used dissolver chemicals. The new dissolver chemistry has significant chelating ability for sulfide scales as well as other ‘standard’ scale types including, calcium carbonate and calcium sulfate. The new product offers an effective multi-functional solution to dissolution of heterogeneous scale deposits. The paper concludes with a case history of field application summarizing in detail the parameters of the field deployment and various KPIs used to measure success. The application is unusual as it was performed using a continuous injection method into an online system.

Traditional test methods to evaluate dispersion and inhibition of paraffin wax, which are mainly based on wax gelation and deposition, often fail to distinguish and differentiate between classes of chemistries at a reasonable resolution. Recommended products based on such lab screenings sometimes have a difficult time proving success in the field. The rush for oil production from unconventional shale plays in North America create a need for quick and elaborate testing to effectively evaluate new products for prevention and remediation of known paraffin wax issues. This paper will present a progress made in this area. For our studies a model oil system was used, which consists of field wax deposit dissolved in kerosene. Testing with a model oil allowed us to focus on the chemistries that are effective against paraffin chains known to cause issues. Several different testing conditions were used to push the ability of the chemistries to function. Light scattering was used to monitor transition from turbidity to sedimentation of paraffin wax from bulk solution under static or dynamic conditions. A total of twelve compounds from three classes of polymers and three classes of surfactants were used in treatment of these oil systems. With this new lab testing methodology, we have been able to discover new insights on the chemistries used for paraffin wax dispersion and inhibition. In contrast to methods which only measure the end point, light scattering and transmission methodology provides system details at time intervals of 30 sec or higher. The method also allowed us to differentiate chemistries based on their impact on the separation index and sedimentation rate of targeted paraffin chains under stressed conditions by forced precipitation. It was found that certain classes of chemistries are more suited for dispersion and inhibition of waxy condensates once system passed the critical point, while others fail over time. This new approach is fast and versatile and must be used as part of a suite of lab and field screenings for product development and recommendation. New methodology based on light scattering and transmission of oil systems can provide details not seen before on colloidal stability or instability of waxy crudes under stressed conditions. The method gives an even greater insight to how different chemistries function to mitigate known paraffin issues. Quantitative and reproducible data are obtained allowing faster screening of various chemistries and enhancing product development for new and aging fields.

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Transportation of waxy crude oils and mitigation of wax deposition are major challenges especially in regions with cold climate. A viable solution for minimizing organic precipitation and fouling in pipelines or storage tanks is the use of inhibitors and dispersants, however, often those pour point depressants (PPDs) have their own challenges due to their own high product pour points. To overcome these issues a series of high active winterized polymer micro-dispersions were developed. Composition and physical properties of several light to heavy waxy crudes were fully explored based on SARA analysis, wax content and paraffin carbon chain distribution. Performance of candidate chemistries from four major classes of polymeric paraffin inhibitors were studied using industry standard methods. Selected high performing chemistries were processed into micro-dispersions using solvents and surfactants under high shear/ high pressure blending. The new polymer micro-dispersions (MDs) were characterized by their pumpability and stability at cold climates. Series of pour point measurements, rheology profiles and wax deposition tests were carried out for performance comparison of MDs to standard polymers in solution. Processes developed here were versatile to convert polymers from all classes of chemistries into micro-dispersion. Binary and ternary polymeric dispersions were also created showing synergistic effects on the pour point reduction and inhibition of wax deposition of the selected challenging crude oils. The performance of the new polymer micro-dispersions was found comparable to superior with standard polymers in solution. Hence, it was possible to create pumpable inhibitors for extreme cold climates without compromising on performance. The systematic approach used here allowed development of more customized solution based on crude characteristics and desired performance. Micro-dispersions were found stable for long term storage in temperatures ranging from -50°C to +50°C. Multiple global field trials are on-going with very positive results demonstrating early success in lab-to-field deployment. Based on lab and field data, this paper demonstrates that highly active micro-dispersed polymers can perform at significantly lower dosage rate when compared to winterized polymers in solution. Cold storage stability and pumpability eliminated the needs for heated tanks and lines reducing operation and capital expenditures.

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.