High-Permeability Carbonate Zones (Super-K) in Ghawar Field (Saudi Arabia): Identified, Characterized, and Evaluated for Gel Treatments

Abstract

Abstract Super-k (carbonate zones of extremely high permeability) can significantly enhance recovery per well in the Ghawar Field. These zones present a challenge at the onset of normal water arrival as the water contribution from these zones dominates the flow in the wellbore—causing either high water-cut or water loading. As a component of the common practices in Ghawar, water shut-off techniques such as the one described in this paper present an effective mechanism to manage water production. This research project has three objectives. The first objective is to identify and characterize super-k zones. The second objective is to identify chemical blocking agents that can be placed in super-k zones without reducing hydrocarbon productivity. The third objective is to identify an effective technique to optimize the size and the placement of the chemical blocking agents. Concerning disproportionate permeability reduction (DPR), gelant treatments, that rely on the ability of the gels to be placed in the rock matrix adjacent to the fractures and to reduce permeability to water much more than that to hydrocarbons (DPR in the rock matrix); have more significant potential than does application of DPR in the fracture. A high residual resistance factor to oil in the fracture may shut-off oil. Distances of gelant penetration can be predicted by knowing the pressure drop and controlling the gelation time. Gel properties for a strong gel that reduces permeability to water as a function of polymer concentrations can also be predicted. If pressure drawdown is held constant before and after a treatment, calculations suggest that relatively small gelant volumes may be most cost-effective in our case. The cost of water treatment, the initial water production rate, the oil residual resistance factor, and the pressure drawdown have strong effects on the economic benefits derived from this approach. Introduction The Ghawar field is the world's largest onshore oil reservoir in operation worldwide, with peripheral waterflooding used to maintain pressure and sustain oil production. This reservoir is a heterogeneous carbonate, containing faults, fractures and high-permeability zones.[1–5] For effective reservoir management, high-permeability zones must be identified and characterized. These zones have a strong impact on the overall behavior of the reservoir, especially during secondary recovery operations. Therefore, an important objective of this study is to identify and characterize high-permeability zones to:avoid early water breakthrough,increase the well life for oil production,reduce the cost of maintenance and lifting process for oil wells, andreduce the cost of expansion facilities to handle excessive water production. In this paper, we identified and characterized the high permeability zones using core analysis and open-hole flowmeter data. A modified version of the Carman-Kozeny equation proposed by Amaefule and Altunbay[6] was also used to identify and characterize high-permeability zones in the heterogeneous carbonate reservoir. We also used special core analyses along with open-hole flowmeter results to differentiate between zones in terms of location and lithology.Finally, application of gels to reduce water production from these zones was examined in detail.