Successful Implementation and Effective Hydraulic Fracturing of Jurassic, HPHT and Tight Carbonate Reservoir in the State of Kuwait: A Case Study of an Exploration Well
Authors: Al-Otaibi Fahad , Al-Bader Haifa , Al-Ibrahim Abdullah , Subban Packirisamy , Duggirala Vidya Sagar , Ayyavoo Manimaran 
Published: February 2020

Abstract

Objective/Scope
The objective of this paper is to present a successful acid frac technique applied in a deep HPHT well to enhance the productivity of Marrat reservoir.

Method, Procedures, Process
Jurassic reservoirs in the state of Kuwait are deep, sour and tight with High-Pressure and High-Temperature (HPHT) environment. Challenging reservoir quality like low permeability, low porosity, uncertainty about some natural and induced fractures, high stress, etc limits the productivity development for this reservoir. The subject well was drilled up to 16,790 ft with high-density Oil Base Mud (OBM), upto 17 ppg, targeting Marrat formation to prove hydrocarbon in this area. Formation damage caused due to invasion of high-density mud, using Barite as a weighting agent, into the carbonate reservoir poses a challenge to design a proper stimulation treatment to restore the permeability and to evaluate the real reservoir potential. Since the damage caused by OBM invasion cannot be easily treated, it was decided to stimulate this reservoir either by matrix or fracture stimulation. The subject well was tested with Drill Stem Test (DST) and perforated in underbalance condition using TCP gun. Acid treatment was performed with 28% emulsified acid solutions to gain the deep wormhole penetration in order to enhance the well productivity. Pre and Post stimulation flow measurement confirmed a slight improvement in productivity. But still there is a scope for increasing productivity further more. Based on the test results, it was decided to Hydraulic Frac the Jurassic reservoir to achieve the expected potential.
A detailed study was carried out to identify reservoir quality and completion challenges that limit the development of reservoir potential and to recommend remedial mechanism, acid or proppant frac, to improve the well productivity. Based on the analysis, acid frac design and procedure was established to gather data and improve productivity from Marrat reservoir. Prior to the main fracturing treatment, a data-frac was conducted to determine reservoir parameters such as fracture extension pressure, fracture closure pressure and instantaneous shut-in pressure. Based on data-frac results, acid frac was successfully executed and the well productivity was tremendously improved.

Results, Observations, Conclusions
High injection surface pressure of 13,800 psi and high leak-off was observed during main acid treatment due to the tight nature of the formation that resulted in low fluid efficiency and relatively short etched fracture length. Acid fracturing treatment was carried out successfully without encountering any major operational issues. The post-acid frac production results show significant improvement in productivity Index(PI) and 3-4 folds increase in production comparing to main acid treatment results. Post-frac analysis was carried out on the sustained production from the Jurassic reservoir.

Novel/Additive Information
Improvement in well productivity after the acid frac stimulation confirmed the well potential and supported exploration group to achieve the reserve target.