This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 183558, “A Breakthrough Water-Shutoff System for Super-K Zones in Carbonate Ghawar Field: Adsorption and Polymer System,” by Ayman R. Al-Nakhli, SPE, Mohammed Bataweel, SPE, Ayman Almohsin, SPE, and Hameed Al-Badairy, Saudi Aramco, prepared for the 2016 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 7–10 November. The paper has not been peer reviewed.
Excessive water production from hydrocarbon-producing wells can adversely affect the economic life of the well. The major challenge for water control in carbonate reservoirs is polymer bonding to the rock surface. Most commercial products are designed for sandstone formations, and most polymers will not strongly adsorb to carbonate reservoirs. A new water-shutoff polymer system has been developed for carbonate formations and shows great stability.
Introduction
The objective of the project was to develop additives to be used as a smart sealant that can be used to control unwanted water production. Treatment of water associated with hydrocarbon production is a key goal because the production of salt water has resulted in serious environmental issues. Excess water production makes a well unproductive and economically inefficient, leading to early abandonment of wells and reduction in hydrocarbon production.
Reservoir heterogeneity is the single most important cause of low oil recovery and early excess water production. Gel treatments have been used extensively in field applications to improve oil recovery and suppress water production. Gel treatments at injection wells to plug water thief zones are a proven cost-effective method to improve sweep efficiency. In addition, gel treatments reduce excess water production during hydrocarbon production.
The initial focus of the project was to develop materials that impart relative permeability modification in naturally fractured carbonate reservoirs with permeability from 1 to 3 darcies in the Ghawar Field, which is a heterogeneous carbonate.
Development
Chemical functionality that can bond strongly to the target carbonate reservoirs is an extremely important component of the development of the smart sealant. Methodologies to provide strong adhesion to carbonate surfaces, and hence to formations, have been developed using silicon-containing molecules. In addition, the additives developed have shown promise on both water- and oil-wet surfaces.
The list of chemicals that could be assessed as additives to bond to the carbonate surface was long, so the team developed a laboratory-based screen to test adhesion rapidly. For the first screens, calcium carbonate powder was a good model because it is readily available and is a major constituent of carbonate reservoirs. The experiments involved taking accurately weighed samples of calcium carbonate and exposing them to different target additives that could potentially bond to the surface. Subsequently, the samples were washed extensively with water to remove any materials that had not chemically adhered to the surface, were dried under reduced pressure, and finally were reweighed. Any significant weight increases were indicative of bonding.
