A Case Study to Develop Contaminated Tight Sour Oil Reservoir Form South Sultanate of Oman
Authors: Al Harrasi A. M. , Al Kalbani M. , Al Tobi K. M. , Oyang Y. , Lefeber T. , Al-Jarradi S. , Al-Shabibi A. , Smirnov D. A. , Harrasi A. , Al Ghammari A. , Al Saadi Z. 
Published: February 2024

SAMA is a contaminated field located in Southern Oman producing from a tight salicylate reservoir with light, sour oil, and H2S/CO2 contents of 1 and 2 mol%, respectively. It is more than 3,000 m deep, encapsulated in salt and over-pressured. The field is studied to assess its development potential using unconventional hydraulically fractured producers following positive initial results from two proof-of-concept wells. This paper describes the results extending the proof of concept into further field development, to mature commercial volumes, and meets project’s value drivers.

This project has no similar analogue and learnings from close analogues were taken, considering differences, and applying integration of data from different sources and disciplines. It is developed through an agile phased approach to fast-track development, de-risk uncertainties and harness potential opportunities. The project incorporated and calibrated proof-of-concept well results, evaluated analogue field performance, explored the development solution space and optimal project decisions in line with project drivers. The concept of unconventional fracs to improve flow behavior is used to optimize the well spacing and total number of wells, considering the uncertainties of back produced frac fluid and the potential of halite scale precipitation. Proof-of-concept well hydraulic fracture parameters were matched in Ghofer and subsequently calibrated against well surveillance data using 3D dynamic reservoir simulation sector models in a Computer Modelling Group simulator. Calibrated models along with analogue field performance information were subsequently used to generate production forecasts to determine optimum project decisions.

The two unconventional hydraulically fractured wells were successful. The reservoir coverage increases threefold compared to conventional fractured wells, and oil recovery is expected to be fivefold against a higher Tubing-Head-Pressure. Unconventional hydraulically fractured wells create longer fractures than conventional ones and proved to deliver economically viable oil rates. Learning from these, the decision is to use unconventional frac, cleaner HVFR frac fluid, around 15-25% fracture conductivity damage. Optimal Unconventional frac design and well spacing were considered dependent and assessed in combination. To further optimize frac design, a longer-term trial plan will be implemented. Some decisions related to well design, completion, and material were reached, considering production conditions, to deliver commercial oil safely for such contaminated field with opportunities of $2.9 mln saving per well. Considering wide enough options and narrow down the selection based on a rigid decision-making approach, while integrate dependent decisions, is a key element to reach to quality development decisions.

The authors have summarized the successful results from two unconventionally fracked wells, and field development decisions related to wells number, optimal spacing, frac and wells completion design that should be taken in an integrated manner. Different field development opportunities and decisions were discussed in detail. Considering the immense challenges while studying to develop the field, multiple learnings can be taken and replicated in similar contaminated fields.