No abstract

No abstract

No abstract

The ultrahigh temperature (150–200 °C), pressure (1000–1500 bar), and TDS (over 300 000 mg/L) encountered in oil and gas production from deepwater pose significant challenges to scaling prediction and control. An apparatus has been built to test scale formation at temperature up to 250 °C and pressure to 1700 bar (24 000 psi). The study expands the current knowledge of Barite (BaSO4) solubility to the condition of high temperature, pressure, and ionic strength. By fitting Pitzer’s model to experimental solubility data, this study also provides a feasible approach to assess the temperature and pressure dependence of virial coefficients in the Pitzer’s equations of ion activity coefficients through measurement of mineral solubility. The prediction of Barite solubility made by the Brine Chemistry Consortium software ScaleSoftPitzer (SSP) that has incorporated the newly developed coefficients is consistent with experimental measurement.

No abstract

Phosphonates are widely used scale inhibitors in oilfields for scale control. In this study, crystalline-phase calcium phosphonate nanomaterials were prepared from amorphous silica-templated calcium phosphonate precipitates that were matured into crystalline phases by a simple diafiltration process. The crystalline solids were further dispersed into a surfactant solution to form a nanomaterial suspension (nanofluid) by ultrasonic treatment to expand their use in the delivery of phosphonate inhibitors into formation core materials for scale control. The physical and chemical properties of the synthesized crystalline nanomaterials were characterized by chemical analysis, electron microscopy, X-ray diffraction, infrared microscopy, and thermogravimetric analysis. The transport of the synthesized nanofluids through calcite and sandstone media was investigated using laboratory column breakthrough experiments. The nanofluids were transported through these media at different breakthrough levels. The experimental transport data were correlated using an advection−diffusion equation, as well as colloid filtration theory, with emphasis on the effect of flow velocity on the particle transport. The maximum transport distance of the nanomaterials in porous media was estimated based on the flow velocity and the particle attachment efficiency.

With the advance of new exploration and production technologies, oil and gas production has gone to deeper and tighter formations than ever before. These developments have also brought challenges in scale prediction and inhibition, such as the prevention of scale formation at high temperatures (150-200 C), pressures (1,000-1,500 bar), and total dissolved solids (TDS) (>300,000 mg/L) commonly experienced at these depths. This paper will discuss (1) the challenges of scale prediction at high temperatures, pressures, and TDS; (2) an efficient method to study the nucleation kinetics of scale formation and inhibition at these conditions; and (3) the kinetics of barite-crystal nucleation and precipitation in the presence of various scale inhibitors and the effectiveness of those inhibitors. In this study, nine scale inhibitors have been evaluated at 70-200 C to determine if they can successfully prevent barite precipitation. The results show that only a few inhibitors can effectively inhibit barite formation at 200 C. Although it is commonly believed that phosphonate scale inhibitors may not work for high-temperature inhibition applications, the results from this study suggest that barite-scale inhibition by phosphonate inhibitors was not impaired at 200 C under strictly anoxic condition in NaCl brine. However, phosphonate inhibitors can precipitate with Ca 2þ at high temperatures and, hence, can reduce efficiency. In addition, the relationships of scale inhibition to types of inhibitors and temperature are explored in this study. This paper addresses the limits of the current predition of mineral solubility at high-temperature/high-pressure (HT/HP) conditions and sheds light on inhibitior selection for HT/HP application. The findings from this paper can be used as guidelines for applications in an HT/HP oilfield environment.

Summary A surfactant-assisted synthesis route was developed to form nanometer-size metal-phosphonate particles. The purpose is to develop a new treatment method for scale control. Aqueous solutions of calcium chloride and zinc chloride were mixed with a basic solution of either diethylenetriamine-penta (methylene phosphonate) (DTPMP) or bis-hexamethylenetriamine penta (methylene phosphonate) (BHPMP) in the presence of tetradodecylammonium bromide (TTAB) or sodium dodecyl sulfate (SDS) surfactant to form nanometer-size particles. The physical and chemical properties of the fabricated nanoparticles have been evaluated carefully. A large number of fabrication procedures are screened, and only those that yield metal-phosphonate particles of 50–200 nm in diameter are evaluated further. Furthermore, these nanoparticles should meet the criteria of forming stable suspension for more than 1 week at 70°C in 2% KCl solution. The nanoparticles can travel through the porous media and be deposited into the formation during a shut-in period. When production resumes, the inhibitor nanoparticles are dissolved into the produced fluid to prevent scale formation. The potential application of synthesized nanoparticles in scale treatment in oil fields has been tested by laboratory squeeze simulations, in which the nanoparticles were placed a distance away from the injection port, retained by the porous media, and returned slowly during flow-back with synthetic brine. The retention and long-term-flowback performance of metal-phosphonate particles is reported.