Engineered Perforation and Tubular Movement/Stress Modeling in Optimization of Complex Hydraulic Fracturing Application in Deep, Tight, Sour and HPHT Carbonates in North Kuwait
Authors: Al-Saeed A.. , Al-Mefleh K.. , Al-Awadhi M.. , Pradhan San. P. , Fidan E.. , Al-Failakawi A.. , Abdelbagi Mamoun. E. , Samuel I 
Published: October 2017

Producing hydrocarbons at appraisal and development targets from deep, sour, over-pressured and HPHT carbonates in North Kuwait has been a challenge driven by the complex reservoir heterogeneity as well as the damage induced by the use of barite-laden heavy oil-based mud (OBM) in drilling and during installation of production tubing as completion fluid. Due to the tight formation properties and the added damage induced by OBM, matrix acidizing does not always deliver hydrocarbons at economic rates. Such zones require hydraulic fracturing under challenging conditions imposed by the wellbore limitations, such as high degree of deviation, smaller tubing as the frac string, and length limitations of the seal-bore assembly, as well as the on-site presence of a deep drilling rig to complete the tests effectively and on-time.

Tubing conveyed perforation (TCP) and wireline perforation techniques require wells to be subdued prior to the installation of final completion due to the over-pressured reservoir conditions and requirement to perforate with as large guns as possible. Both of these techniques have proven less then efficient as the flow tests performed before and after running final completion historically indicated significant drop in production of hydrocarbons. Therefore, a gun hanger shoot-and-drop perforation system was customized to facilitate underbalance perforation and immediate well clean up with no further well-kill requirement whilst still utilizing optimum gun size for better perforation geometry.

As an added challenge, the requirement to hydraulically-frac the tight carbonates necessitated modeling and design of tubular movement, stress analysis & drag modeling in the highly deviated case described in this paper. Determining the operational pressure envelope to complete the hydraulic frac treatment safely and effectively (operations pressure management) was the critical success factor in the placement of large acid hydro-frac without jeopardizing the wellbore (PBR seal) integrity. Customized "surfaceadjusted" weight of tubing slack off methodology was developed and implemented, resulted in maintaining safe operational conditions during the hydro-frac where the wellhead treating pressures exceeded 13,000 psi.

Because of the specific perforation technique and analytical approach required for optimal treatment pressure management, a complex data-frac program followed by a large and customized acid hydro-frac program were successfully implemented with the facilitative function of the deep drilling rig on the well site.

Collection of critical completions data was achieved and the reservoir deliverability was established while wellbore integrity was maintained. Mechanical formation properties were determined and hydro-frac geometry on effectively connecting to the higher mobility segments of the reservoir was realized. This paper will also outline the future optimization plans based on the learnings from the frac tests conducted in the well.