High Pressure High Temperature Reservoir Fluids with Focus on Scaling and Thermodynamic Modeling

Diana Carolina Figueroa Murcia

Research output: Book/ReportPh.D. thesis

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Abstract

Extensive research to increase the world’s oil reserves is focused on the High-Pressure High-Temperature (HPHT) reservoirs. These reservoirs represent a great opportunity but also a challenge in terms of drilling, extraction operations and safety protocols. The extreme operating conditions and harsh environments of the HPHT reservoirs push the limits of engineering. Developing new materials that can withstand elevated temperatures, highly corrosive atmosphere (e.g. the presence of H2S) and building machinery capable of working at pressures above 690 bars are at the order of the day. Amon gthe cumbersome conditions mentioned, consequences inherent to the exploration activities, such as the rapid pressure drop will cause for example the deposition of minerals. The deposition of materials is referred to as scaling. The occurrence of scaling in oil reservoirs bring adverse consequences such as clogged pipes, malfunction of safety equipment (e.g. the safety valve) and reduction of the production of the well. Nowadays, the sulfide scaling materials are gaining more attention as they require a different treatment for their removal compared to the common scaling minerals found in oil reservoirs. These materials are formed as the product from the reaction between metallic ions (present either in the formation waters or injected brines) and H2S present in the reservoir.The aim of this thesis is to study the solubility of scaling materials, specifically Zinc Sulfide (ZnS), Iron Sulfide (FeS) and Lead Sulfide (PbS) at conditions that resemble HPHT reservoirs. Firstly, the Joule Thomson Effect (JTE) was evaluated to determine the impact of the decompression process on the final temperature of a confined fluid at HPHT conditions. Three different fluids (water, oil andbrine) were included in this study. It was concluded that the increase of temperature for oil at non-isenthalpic conditions is 7.4 °C This represents a reduction of 16.8 °C compared to the final temperature estimated at isenthalpic conditions. Thus, these results show that if the JTE is estimated at isenthal pic conditions the final temperature is overestimated.
This study presents the design of an experimental apparatus at laboratory scale as well as the development of a reliable experimental methodology for measuring the solubility of minerals at HPHT conditions and especially at very low concentrations (trace elements).The designed experimental apparatus is a borosilicate glass set-up for measuring the solubility at temperatures upto 80 °C. Additionally, a High-Temperature Cell made of Titanium was built to perform the solubility experiment at temperatures up to 200 °C and 60 bars. Several drawbacks from published solubility methods were addressed in this study:(1) Anoxic conditions were guaranteed throughout the process,(2) sufficiently long contact time was assured between the solvent and the solute to assure steady state conditions and (3) an adequate analytical technique for measuring trace elements: Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) was chosen. Saturated solutions of theminerals were prepared and then the aqueous solution was analyzed using ICP-OES. Afterwards, the experimental data were used for adjusting the Extended UNIQUAC model to predict the solubility ofsulfides by means of thermodynamic calculations. The prediction of the occurrence of the scaling materials in an oil reservoir is a foremost tool for the operator of a well. The results showed that the Extended UNIQUAC model can represent the solid liquid equilibrium of Zinc Sulfide and Iron Sulfide up to 100 °C. Difficulties were encountered for representing the solid-liquid equilibrium of the PbS aqueous system. The inclusion of complexes into the speciation equilibrium model is required to achieve good results. This study is a step towards understanding the behavior of sulfide scaling materials at high-temperatures and high-pressures.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages175
Publication statusPublished - 2018

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