Aromatic-based solvents, including benzene, toluene, xylene (BTX) and their derivatives have been successfully applied for asphaltene removal from downhole and surface facilities. These solvents are considered non-environmentally friendly due to their associated health and safety concerns including high toxicity, low biodegradability and low flash point. Currently, more attention has been given in the oil industry to develop environmentally friendly asphaltene solvents. This paper examines several environmentally friendly solvents derived from natural precursors to dissolve asphaltene, wax and combined asphaltene/paraffin organic deposit. A group of plant-derived and terpene-based asphaltene solvents with flash points ranging from 50.5 to 136 °C was examined in this study. Extracted asphaltene from a crude oil and wax obtained from distillation were used to assess solvency power of these solvents. Solubility of organic deposits containing more 42 wt% asphaltene with associated paraffin was evaluated in these solvents. The performance of these solvents was examined as a function of soaking time and temperature. These environmentally friendly solvents showed comparable solvency power to toluene. The lowest flash point solvent exhibited the highest solvency power for asphaltene while the opposite relation was observed for the wax sample. The lowest flash point (50.5 °C) solvent was able to dissolve 91 wt% of the asphaltene sample after soaking for 2 hours at ambient temperature compared with the highest flash point solvent (136 °C), which dissolved only 7.4 wt% at the same conditions. For wax, the solvent with the second highest flash point (132 °C) was able to dissolve 97 wt% of the wax while the solvent with a flash point of 50.5 °C was able to dissolve 85.5 wt% at ambient temperature and after 2 hours. Some of the examined environmentally friendly solvents showed very high dissolution power to organic deposits composed of asphaltene and paraffin where a solubility of 96 wt% was obtained at 80 °C and after a soaking time of 6 hours. The paper will discuss these results in detail.

The drilling fluid in a vertical well may only be in the pay zone for few hours while in a horizontal well the time can be measured in weeks. This can cause a significant formation damage problem that has the potential for reducing productivity in horizontal wells during drilling operations. A common practice following drilling operations involove filter cake removal operation followed by displacement of wellbore fluids by completion fluid in order to prepare the well for production operations. Presence of drilling fluids in horizontal wells for several weeks is not considered in the design for cleaning fluid recipies targeting drill-in fluid damage. The filter cake buildup time affect its physical characteristics and thus, on the removal process. This study focused on the characterization and the cleanout of the filter cake during the different buildup stages that may occur in the horizontal section. The focus of this study is to highlight the effects of not promptly removing the filter cake. Filter press instrument was used to simulate filter cake formation on the wellbore wall at 500 psi and 300°F. The filter cake formation process was performed using oil-based drilling fluid at different buildup times (i.e., 3 hours, 3 days and 3 weeks), under 500 psi and 300°F. The comparison of the different scenarios showed that a thicker filter cake was formed with buildup time (up to 2.5 inch after 21 days). The CT scan results showed that the heterogeneity increased up to 4 layers and the solubility of in the cleanout fluid decreased to 4% by weight.

Guar and its derivatives are the most commonly used gelling agents for fracturing fluids. At high temperature, higher polymer loadings are required to maintain sufficient viscosity for proper proppant carry and creating the fracture geometry. To minimize fracturing fluids damage and optimize fracture conductivity, it is necessary to design a fluid that is easy to clean up by ensuring proper breaking and sufficiently low surface tension for flow back. Therefore, breakers and surfactants must be carefully selected and optimally dosed to ensure the success of fracturing treatments. In this study, two fracturing fluids were evaluated for moderate to high temperature applications with a focus on post-treatment cleanup efficiency. The first is a guar-based fluid with a borate crosslinker evaluated at 280°F and the second is a CMHPG-based fluid with a zirconate crosslinker evaluated at 320°F. The shear viscosities of both fluids were tested with a live sodium bromate breaker, a polymer encapsulated ammonium persulfate breaker and a dual breaker system combining the two breakers. Different anionic and nonionic surfactant chemistries (aminosulfonic acid and alcohol based) were investigated by measuring surface tension of the surfactant solutions at different concentrations. The compatibility of the surfactants with other fracturing fluid additives and their adsorption in Berea sandstone was also investigated. Finally, the damage caused by leak-off for each fracturing fluid was simulated by using coreflooding experiments and Berea sandstone core plugs. Lab results showed the guar and CMHPG fluids maintained sufficient viscosity for the first two hours at baseline, respectively. The encapsulated breaker proved to be effective in delaying the breaking of the fracturing fluids. The dual breaker system was the most effective and the loading was optimized for each tested temperature to provide the desired viscosity profile. Two of the examined surfactants were effective in lowering surface tension (below 30 dyne/cm) and were stable for all tested temperatures. The guar broken fluid showed better regained permeability (up to 94%) when compared to the CMHPG (up to 53%) fluid for Berea sandstone. This paper outlines a methodical approach to selecting and optimizing fracturing fluid chemical additives for better post-treatment cleanup and subsequent well productivity.

Sludge formed downhole in the production interval can be classified into crude oil-based or mud-based sludge. Sludge obstruction may result in partial or total loss of well productivity. Oil-based mud is commonly used in drilling of the pay zones in sandstone formations as a less/non damaging fluid. Oil-based mud typically contain emulsifier, viscosifer and other additives including polymer blend and calcium carbonate to serve different functions. Presence of emulsifier may increase emulsion tendency upon interaction with downhole environment. The resulting emulsion might be tight to an extent that a thick sludge is formed which can impair well productivity. Similarly, oil-based sludge may form from oil/water interaction in presence of emulsifiers, asphaltene, wax, solids, shear, etc. Identification of the sludge material will help in development of an effective chemical treatment to remove formation damage and restore well productivity. In this study, an extensive laboratory work was conducted to explore potential interactions of different downhole environment contaminants/factors on formation of oil-based and mud-based sludge. Typical mud-based and crude oil-based sludge samples were characterized using different analytical techniques including solvent extraction, XRD, TGA, ICP and viscosity. The results showed that the mud-based sludge sample contained calcium carbonate, dolomite quartz as the main components in the inorganic phase while the organic phase include polymers and oil. The oil-based sludge sample contained mainly water (82 wt%) with some solid particulates and asphaltene in the organic phase. Analysis of supernatants generated from solubility tests conducted for the mud-based and oil-based sludge samples revealed in addition to the high amount of calcium presence of iron in considerable amount (nearly 1,000 mg/L). Interaction of ferric chloride, quartz with an invert-emulsion mud was investigated. A significant increase in viscosity was observed upon incorporation of these contaminates with the mud sample. Iron ions in the aqueous phase tended to stabilized emulsion. This paper presents in detail mechanisms of mud-based and crude oil-based sludge formation upon interaction with environment. It also examined several chemical formulations for removal of mud-based and oil-based sludge samples.

Fracturing fluids are normally injected at high rates and pressures to break the reservoir rock, where proppants ideally are suspended during fluid injection. High strength ceramic proppants are used to overcome hash environments (i.e., high closure stress and temperatures). Advancements in proppant manufacturing further added several characteristics to the proppants, such as self-suspending, multi-phase flow enhancer, and multifactional proppants. The objectives of this study were to compare the performance of HSP and ULW ceramic proppants though proppant characterization, wettability measurements, settling behavior, acid solubility, proppant pack conductivity, and proppant crush resistance. Fracture cell was used to measure the proppant pack conductivity. Proppant crush resistance was conducted using hydraulic uni-axial loading frame. XRD and XRF were used to characterize proppant samples. Solubility in HCl solutions was examined. Elemental analysis was conducted using ICP. Light transmission and backscattering technique was used to compare the settling behavior of proppant samples. Drop Shape Analyzer was used to measure the contact angle on the surface of proppant samples. The highest performance proppant among the five-examined proppants was proppant P-1. This was based on the conductivity values obtained, the correlation between conductivity and fines generated, settling behavior, and solubility in HCl acids. Proppant P-5 exhibited non-wetted properties for both water and condensate fluids. ULW proppants (i.e., P-7 and P-8) showed significantly improved suspension properties over the examined HSP proppants. The solubility of the HSP proppants in HCl acid depended on the acid concentration, soaking time, surface area. The solubilities obtained was up to 10 wt% in concentrated HCl acids. High concentrations of Fe were observed in concentrated acid solution (i.e. ~1800 mg/l). Proppant pack conductivity values for examined proppants were relatively similar except for proppants P-3 and P-5.A linear correlation was found between wt% of fines generated and proppant pack conductivity.