Producing hydrocarbons at appraisal and development targets from deep, overpressured, high pressure/high temperature (HPHT) Jurassic carbonates in Northern Kuwait has been a challenge as a result of the complex reservoir heterogeneity. Because of the tight carbonate formation properties, matrix acidizing does not always deliver hydrocarbons at economical rates; in this scenario, hydraulic fracturing is required. Hydraulic fracturing, however, presents placement and activation challenges as a result of the wellbore construction limitations and a complex tectonic setting/high stress environment. The zone of interest in this dolomitic reservoir was identified as an acid fracture candidate because of the immobility of fluids identified during multiple pressure sampling tool attempts, despite a reasonable valuation of the log-computed porosity and permeability in the range of approximately 10% and 1.1 md, respectively. In addition, solid hydrocarbons (bitumen) were reported in the cuttings samples, which indicates the possibility of in-situ conductivity damage. The well trajectory was designed as a high angle deviated well to maximize the reservoir exposure, with a maximum inclination of 49 to 50° through the zone of interest. The reservoir was drilled at a slight overbalance with 13.0 ppg of oil-based mud, using mud weight management techniques to minimize the formation damage. The highly deviated wellbore and the highly anisotropic stress regime complicated the effective design and placement of the acid fracturing treatment. As an added challenge, the operation had to be completed within a very short period because of the high cost of the deep drilling rig on site to facilitate the operation. The hydro-fracture field case was built on the analyses of the open hole logs, 1D geomechanical earth model, and a customized data-fracture suite to meet the data acquisition needs, followed by the design and calibration of an acid hydro-fracture treatment using a pseudo3D grid-based fracture modeling and calibration software. A solids-free dynamic diversion schedule was built and field-laboratory level fluid design tests were conducted to reach the most optimal design possible. A robust and operationally pragmatic fracture program was developed and implemented successfully in a very short notice period. The mobility of the formation fluids was established, leading to a critical understanding of this sour unconventional carbonate flow unit. Data fracture analyses and a customized acid fracturing technique described in this paper are the first of its kind in the deepest parts of the Northern Kuwait sour gas basin. A collection of completions data has proven critical in terms of reservoir deliverability aspects and in the calibration of the mechanical formation properties, leading to a better understanding of the hydro-fracture geometry and how to effectively connect to the higher mobility segments of the reservoir. This paper also outlines the future optimization plans based on the lessons learned from the fracture tests conducted in the well.

Appraisal program of the deep gas/light oil from unconventional reservoirs in North Kuwait is strategically important to secure the challenging hydrocarbon production targets of Kuwait Oil Company (KOC). A very deep high-temperature/high pressure (HT/HP) dolomitic formation is at approximately 15, 000 ft (vertical), poses complex completion and producibility challenges. Exhaustive log suite and core analyses confirm some porosity development and gas shows. Unlike the proven carbonates up-hole in the same asset, the deepest dolomite units have extremely low permeability, and may not flow unless enhanced by a natural fissure network and/or hydraulic fracturing. Only a few wells have been attempted for completion in these deepest dolomite layers, which failed to flow even after matrix acidizing treatments. The effective completion design will require good understanding of formation mechanical properties and fluid leakoff behavior, leading to optimal horizontal wells to maximize reservoir exposure completed with multiple hydraulic fracturing treatments to establish hydrocarbon production at commercially acceptable rates. Therefore, properly designed and effectively executed extensive fracture diagnostic tests are critical in the current pre-appraisal stage. In addition, multiple acid-fracturing treatments have already contributed to the understanding of fracture geometry development and fracture flowback characteristics. A fracture diagnostics workflow was developed and deployed to appraise the deepest dolomite layers. Critical fracture mechanics data were collected and analyzed. The main fracturing treatments have also yielded crucial results, which will help the design team in optimizing the horizontal well completions. This comprehensive workflow can be successfully applied in characterizing challenging formations elsewhere where the well and regional data are limited in the appraisal of similar light oil/tight gas-bearing unconventional carbonates.

The proper fracture stimulation of high-pressure/high-temperature (HP/HT) carbonate formations completed with horizontal wellbores is a challenging task for any operator or service company, particularly because of concerns associated with HP/HT, acid reactivity, completion and production equipment corrosion, and acid distribution. The case history presented in this paper describes the performance of an acid fracture intervention in a HP/HT well where, because of a number of problems encountered during the well construction stage, this intervention was the last procedure considered to evaluate the productivity of a Marrat formation well. In view of the stimulation challenges encountered, the architecture of the wellbore, and the intervention stimulation requirement to evaluate the productivity of the horizontal well completed in the Marrat formation, it was necessary to change the proppant fracture stimulation technique originally planned. Instead, it was decided that a selective acid fracture stimulation would be performed in the prospective part of the horizontal section where three long perforation clusters had been placed. Acidizing fracture stimulation was performed in one intervention using a next-generation liquid and soluble solid diversion system that enabled the generation of one selective fracture per perforation cluster. The planned acidizing fracture stimulation process was implemented properly in the field in accordance with the design constraints. The reactive fluid system diversion and the generation of a new fracture when the diversion system reached the perforation were clearly observed. The post-acid fractured well productivity index (PI) showed the high quality of the stimulation performed in a challenging environment, demonstrating the effectiveness of the new diversion system for creating selective fractures in a horizontal wellbore with multiple perforation clusters. Considering the well's architecture, HP/HT nature, and single intervention requirement, the case study documented in the paper can be helpful in the decision-making process when selecting a proper stimulation technique for challenging conditions. The effectiveness of the new diversion systems is also discussed.