Scale prevention is important to ensure continuous production from existing reserves that produce brine. Wells could be abandoned prematurely due to poor management of scale and corrosion. The objective of this paper is to present an overview of scale prediction and control and the current research at Rice University to solve these problems. In this paper, the challenges of scale prediction at high temperature, pressure, and TDS are reviewed. An accurate model to predict pH, scale indices, density, and inhibitor needs at these conditions are discussed. First, the various scale types found in oil and gas production and the condition under which they form are discussed. Secondly, the relationship of pH, alkalinity, organic acids, carbonates and CO 2 distribution is discussed. Thirdly, the temperature, pressure, TDS dependence of the thermodynamic equilibrium constants and activity coefficients is discussed. Lastly, the accuracy of a scale prediction program and its application is discussed. Based on a simple propagation of error estimation, the overall estimated error for calcite SI is ± 0.1. The program has been validated with literature solubility data for 6 minerals, pH data at 25 and 60 C, and density of high TDS solutions and up to 12.7 lb/gal weighting fluid.
IntroductionBy all accounts, oil and natural gas will be the major components of global energy production for decades to come. Although proved oil and gas reserves may be declining, oil and gas production can increase with the development of new technologies to extract energy from unproved reserves and improved economics of production from both known reservoirs and marginal fields. For example, oil and gas have gone to deeper and tighter formation with the advance of new production technologies. These new developments in oil and gas production also bring challenges in scale prediction and inhibition, e.g., at high temperature (150-200ºC), pressure (1,000-1,500 bars) and TDS (>300,000 mg/L) commonly experienced at these depths. Brines from different zones are often mixed in the production tubing, subsea tieback or a common facility. Often the oil, gas, and brine composition in each zone is quite different and consequently will cause significant scaling. Steam, seawater or alkaline surfactant flooding are employed to mobilize residual or heavy oil. Many of these cost saving measures can result in significant scaling problems. Scale prediction, control and treatment are vital to the success of these processes.A major component of scale and corrosion management is the ability to accurately predict the brine chemistry, pH, and scaling tendency of a production system. The typical variables in oil and gas fluid components are shown in Table 1. Due to the complexity of the system, scale prediction is not as straight forward as one might imagine. In this paper, we attempted to address the following: (1) the theoretical background of scale prediction and reliability; (2) the impact of brine salinities, composition, and temperatures on pH, scale and corrosion; (3)...