Horizontal Multistage Acid-Fracturing Formulates Development Strategy in Tight Tuba Carbonate Reservoir, North Kuwait
Authors: Al-Mosaileekh Safia , Saleem Eman , Abd El-Aziz Sabry , Abdel-Basset Mohamed 
Published: March 2019

Tuba is tight carbonate reservoir and one of largest Upcoming Reservoirs in North Kuwait Sabriyah field and subdivided to three main reservoir units (upper, middle and lower). Tuba, though discovered in the 60's, is still relatively under-exploited presently with only ±10 active oil producer wells with very low total production rate compared to other major reservoirs in same field. High reservoir heterogeneity, tightness, and poor fluid properties necessitate the application of fracturing stimulation technology to maximize Conductivity and hence recovery enhancement. Recent technologies in multistage acid Fracturing executed successfully covering multiple layers as first time ever in one of existing two Tuba horizontal wells.

The well under study is highly deviated, completed as barefoot in the Upper Tuba reservoir, intersecting multiple sub-layers. Following the positive results of acid fracturing treatments in offset Tuba's vertical wells, the candidate well was selected for first multistage acid fracturing in horizontal wells, to setup the reservoir development plan ensuring high production potential with most cost-effective drilling and completion strategies. Rig-less 5-Stages Acid Fracture treatment was executed in flawless operation. Many technical and operational challenges were faced (Geo-mechanics, stages selection and design, cementing 7in liner) and properly handled within integrated teams with lessons learned are to be considered in next designs and executions. Initial post multistage acid Frack short term production showed productivity improvement by approximately 5 folds of pre-stimulation production. The well showed high decline in production rate within the first one-year production post fracturing stimulation. However, analysis showed that the decline mainly was caused by reservoir depletion rather than fracture conductivity deterioration. The well is under close monitoring for stabilization (rate and pressure). Horizontal PLT is planned to evaluate inflow profile from individual layers to improve next designs.

Despite the close results yilded from the multistage acid fracturing in two horizontal wells compared to the results from 7 vertical wells, it is still early to evaluate stimulation potential of horizontal against vertical wells. It needs more production history and more wells to evaluate long term sustainability.

Water-flooding is planned to support reservoir development and enhancing stimulation sustainability and by turn recovery factory. First pilot water flooding injector well was commissioned in early 2018, but comprehensive waterflooding analysis is not finalized yet.

The initial positive results of first multistage acid fracturing in Tuba reservoir had key contribution to setup Development strategy for the entire TUBA reservoir to expand drilling horizontal wells and complete it with initial multistage fract (MSF) stimulation to maximize reservoir exposure and enhance reservoior productivity that will contribute significantly to the NK production target. Two more horizontal wells were drilled and completed with MSF in late 2018 with initial encouraging enhanced productivity results during cleaning and lifting but were not put yet on production for more comprehensive analysis. ation to improve initial productivity.