Ore-Forming Fluid Evolution of Shallow Polyhalite Deposits in the Kunteyi Playa in the North Qaidam Basin

Polyhalite occurrence in the Kunteyi Playa in the Qaidam Basin has been known for many years. However, the genetic mechanism of this deposit remains unclear. In this study, a typical section in the playa depocenter is selected to study the polyhalite mineralogy combined with the homogenization temperature and composition of halite fluid inclusions in shallow evaporitic strata. The results show that 1) the main evaporite minerals in the strata are halite and polyhalite; no common gypsum is found; 2) analyses of homogenization temperatures of halite fluid inclusions indicate that a higher temperature is needed for polyhalite generation compared with other saline minerals; and 3) the fluid inclusion chemical analysis shows that they are sulfate-type minerals with a shortage of Ca. Thus, it can be concluded that the formation of polyhalite is not related to gypsum replacement, and deep oilfield brines may provide a Ca source and a higher temperature for polyhalite formation, where the mixing and interaction occurred between K- and Mg-enriched sulfate brines and deep Ca-enriched brines under the control of climate and tectonics in the study area. While most polyhalite was generated natively, some formed during secondary generation, which was potentially related to replacement with carnallites or sylvites.

Prevent Failures and Extend Asset Life: A Reliable Onsite Corrosion Inhibitor Residuals Method Using SERS

Asset integrity for oil and gas operations requires reliable chemical information to troubleshoot factors affecting chemical deliverability and performance. Accurate and precise measurement of corrosion inhibitor (CI) concentration in oilfield brine is significant to asset management. However, historically CI residual measurements are extremely problematic due to the surface-active nature of the chemicals which interact with a host of factors that parasitically deplete the CI solution concentration. It is typical to see >100% error on traditional residual measurements especially where dye transfer techniques are concerned. Current methods and sample handling for measuring residuals involves sending samples to a local laboratory for analysis. This time delay can add to the measurement error due to loss of inhibitor species to the sample container or solids that may form in transport. This paper describes the use of a simple, portable, handheld, onsite, nanotechnology-based, residual method to measure CI concentrations in oilfield brines. With more frequent and highly accurate CI residual feedback operators can react to system conditions that threaten to impact asset integrity. Using the CI residual data provided by a rapid, accurate analytical method, operators could extend asset life and prevent failures long before they become critical.

CO₂ Top-of-line-corrosion; assessing the role of acetic acid on general and pitting corrosion

Based on a review of both literature and field data, it is apparent that the role of acetic acid (HAc) in oilfield brines is both extremely complex and somewhat controversial. Although it is commonly believed that the presence of this organic compound enhances both the general and the localized corrosion rate of carbon steel, HAc has recently been reported to also act as a weak general corrosion inhibitor in specific aqueous environments. These observations prompted a study into whether such behavior is apparent in a CO<sub>2</sub> top-of-line corrosion (TLC) scenario i.e. when HAc dissolves into condensed water which forms on the upper internal wall of carbon steel pipelines during wet-gas stratified flow. Four different water condensation rates/temperature TLC conditions were selected to investigate the role of HAc on both the kinetics and mechanism of carbon steel dissolution. A miniature three-electrode setup was developed to characterize the real-time TLC response through the implementation of electrochemical measurements. Surface analysis techniques (microscopy and profilometry) were also performed to complement the electrochemical results. Collective consideration of the corrosion response and condensate chemistry indicates that similar effects were observed compared to those reported in the literature for bulk aqueous environments, in that the introduction of HAc can result in either accentuation or a minimal/inhibitive effect on general corrosion depending upon the operating conditions. The minimal/inhibitive effects of HAc were apparent at a surface temperature of 20.5<sup>o</sup>C and water condensation rate of 0.5ml/m<sup>2</sup>.s as no significant increase in corrosion was observed despite a significant reduction in condensate pH being generated due to the presence of HAc. X-ray photo-electron spectroscopy analysis of the inhibited steel specimen in the presence of HAc revealed the presence of iron acetate on the steel surface which may have been at least partially responsible for the observed inhibitive effect. Extended duration experiments over 96h revealed that both general and localized corrosion are not significantly affected by HAc addition at low temperature whilst the level of degradation increases at higher surface temperature over longer periods.

Diminishing Depth to Water in Cambrian-Ordovician Arbuckle Group Disposal Wells in Kansas

Industrial and municipal wastewater and oilfield brines have been disposed of into the Cambrian-Ordovician Arbuckle Group for decades in Kansas and nearby states in the midcontinent United States. The industrial and municipal wastewater disposal wells (designated Class I disposal wells) are regulated by the Kansas Department of Health and Environment. The oilfield brines are disposed of in Class II disposal wells, which are regulated by the Kansas Corporation Commission. Annual testing of formation pressure and static fluid levels in Class I wells compose a body of data that is useful in monitoring movement of water and fill-up of Arbuckle disposal zones. In western Kansas, the depth to water in wells penetrating the Arbuckle can be several hundred to more than a thousand feet (305 m) below ground surface, but in parts of southern and southeastern Kansas, the depth to water locally can be less than 100 ft (31 m). Furthermore, most Class I wells indicate Arbuckle fluid levels in central and south-central Kansas are rising ~10 ft (~3 m) annually, suggesting that at current disposal rates, the Arbuckle may lose its capacity to accept wastewater under gravity flow in parts of the state in the next few decades, principally south-central and southeastern Kansas along the Oklahoma state line. At present in parts of six Kansas counties along the Oklahoma state line, low-density (~1.0 g/cc or slightly greater density) wastewater in a wellbore does not have a sufficient hydrostatic head by gravity alone to force its way into the more dense resident Arbuckle formation water. In general, Arbuckle formation water flows west to east in Kansas. Arbuckle disposal wells in Kansas collectively dispose of ~800,000,000 barrels (~127,000,000 m3) of wastewater per year, although some of this is recycled from Arbuckle oil production. Declines in oil price since mid-2014 have resulted in less oilfield disposal in the Arbuckle since 2015. The number of Class I wells recording annual fluid rises have also declined since 2015, as has the median of their annual change in static fluid level, but overall, more Class I wells are still recording fluid rises. There is a poor correlation between changes in fluid levels in Class I wells and the volume of fluid disposed in them annually, thereby indicating that more regional characteristics may control water movement in the Arbuckle. More monitoring wells are needed to better understand the movement of water in the deep subsurface and to anticipate any potential problems that may occur with reduced disposal capacity and possible migration of fluids through unplugged or improperly plugged older wells.

The Source, Distribution, and Sedimentary Pattern of K-Rich Brines in the Qaidam Basin, Western China

Potash plays an important role in agricultural production. The Qaidam Basin (QB) in western China is a typical inland evaporite basin, which contains an abundance of K-rich brines, including shallow brines (i.e., surface brines and intercrystalline brines) in salt lakes and deep brines (i.e., pore brines and oilfield brines) in the strata. Significant studies on these brines have been reported; however, the integrated studies on sources of K, its distribution, and the sedimentary pattern of the two brine types are still inadequate. In this study, the K+ concentrations of sixty-four intercrystalline brines from the Qarhan Salt Lake (QSL), the largest playa in the QB, are presented. After combining those results with the major ionic compositions of river waters and deep K-rich brines, and the K+ concentrations of shallow brines in the QB, we concluded that: (1) The K of brines in the QSL is mainly from the high–flux K input by rivers which gain K from silicate weathering, while the “ancient Qaidam Lake” contributed little K to the QSL; (2) the large K flux supplied by rivers, the appropriate concentration degree, and the mixing of river waters and spring waters, cooperatively account for the highest K concentrations of brines in the QSL in the QB. The different river K recharges in different sections and isolated depressions are responsible for uneven K+ concentrations of brines in the QSL. (3) The deep brines are mainly distributed in the western QB. The K source of pore brines is from the interaction of pore water with the overlying evaporite layer. While the K in oilfield brines may be meteoric water, salt dissolution, the mixing of hydrothermal fluids, and the conversion of clay minerals to K-feldspar may consume K in the oilfield brines.

Experimental Investigation of Polyvinylpyrrolidone for Application as a Demulsifier for Water-in-Oil Emulsion

Introduction: Emulsification of produced immiscible mixed liquid of oil and water is a problem frequently recognized in surface production facilities in oil fields. The formed emulsions are required to be demulsified to avoid the negative consequences on piping and processing equipment. Nowadays, chemical demulsification is a preferable method to avoid or retard emulsification during the process of oil treatment. Materials and Methods: In the present study, Polyvinylpyrrolidone, poly-[1-(2-oxo-1-pyrrolidinyl)-ethylene] has been experimentally investigated as a chemical demulsifier for water-in-oil emulsion formulated by mixing a crude oil with synthesized oilfield produced water. Oilfield brines were synthesized by dissolving NaCl in deionized water to obtain salinity similar to the oilfield produced water. The sample of water-oil emulsion was prepared by agitation process at the condition of controlled rpm speed, ambient temperature and concentration of emulsifying agent. Stability of the emulsion was investigated using Turbiscan MA 2000 instrument. Results: The efficiency of the demulsification was screened using Bottle Test. It has been found that Polyvinylpyrrolidone, poly-[1-(2-oxo-1-pyrrolidinyl)-ethylene] accelerates the separation of the emulsion as compared to blank ones (with no addition of PVP). A maximum demulsification performance of the PVP was observed at an optimum concentration of 60 ppm.