Scaling Issue in the Platform Area of Tengiz Field and Preventing Solutions

Abstract

Abstract Even though most wells in the Tengiz Field produce virtually water free oil (less than 1% water cut), inorganic scales have been observed in many wells. Acid stimulation treatment programs for existing wells with deteriorated productivity include implementation of scale inhibitors, however this reactive approach might not always be the best way to proceed. The scope of the paper is to identify the main parameters which increase the probability of scale formation before a well is put on production and proactively treat such wells with scale inhibitors. Previously Tengizchevroil (TCO) has conducted an extensive research project to reduce the need for frequent acid treatments while maintaining well deliverability at sustained rates. Compatibility and core flood tests have been performed to choose the best scale inhibitor, and an extensive surveillance program has been developed to track residual inhibitor concentration to timely plan subsequent stimulation treatments. This paper covers the next step of the study and includes analysis of the recent cases of scale formation including identification of similar properties between the cases to enable forecasting of the tendency of all new wells to encounter scale formation. The study consists of three main steps – analysis of formation water and solid samples, analysis of open hole log data and analysis of production history for Tengiz and Korolev wells. The formation of precipitates is dependent on ion concentration in the water. Analysis of the water composition for each region and formation has been performed to identify which set of parameters increases the tendency to form scale. Solubility of inorganic salts is highly dependent on pressure and temperature changes taking place in the wellbore; therefore, the scale prediction study also includes these factors with the correlation to well region and reservoir properties each well penetrates. Weighted ranks for every parameter have been developed to rank a well after the drilling stage and make a proactive decision on whether scale inhibitor injection should be included in the primary acid stimulation treatment program, or if it should be considered only for reactive acid treatments in case of loss in well productivity. This paper aims to share the best practices in scale inhibitor design, analysis of well parameters at the well completion stage and calculation of well tendency to scale formation. The decision tree for identification of well candidates for proactive scale treatments applicable for the Tengiz field presented in the paper can potentially be used in other carbonate fields.