Chemical Water Shutoff Interventions in the Tunu Gas Field: Optimisation of the Treatment Fluids, Well Interventions, and Operational Challenges

Abstract

Several Indonesian gas fields such as the Tunu field exhibit a specific behavior which causes a rapid decrease of the gas production. At shut in conditions, cross-flows from watered out layers to gas producing layers, were clearly identified as the major cause for gas production impairment. The offloading of water from wells is performed at the preliminary stage of water production and often allows restarting the wells, but in a second stage it is ineffective. The nature of the damage in the gas-producing zones is not entirely understood but it seems to be a combination of at least two phenomena:water adsorption on the high amount of clays present in these highly water sensitive layers (15 to 40 wt %) andwater imbibition due to some capillary pressure experienced in the tightest layers (0.1 to 10 mD). Clay swelling or migration seems also to contribute for this damage but to a lesser extent. Unwanted water along with gas and condensate production from several layers were quantified from multi-rate PLT, to define a strategy for well candidate selection and water shut off interventions. An inorganic gel was then selected to be selectively squeezed into the water-producing layers. The optimization of this fluid and of the preflush fluid required a complete qualification program which aimed at three main objectives:maintain injectivity during the squeeze to allow an entire placement of the fluid,provide, once set an extrusion pressure sufficient to withstand a significant drawdown andgives a treatment's lifetime of one year minimum. Three wells were treated in 2004, following the qualification of the fluids, the selection of candidate wells and the implementation of a complete treatment setup on a barge. This article describes the successes and the failures of some of them, pointing out the need for finely filtered fluids, low viscosity fluids and robust selective placement tools. Introduction The Tunu field operated by Total Indonesia is a north-south elongated structure of 80 km long in the shallow swampy outer edge of the Mahakam delta region of East Kalimantan. It is a giant field of approximately 70x20x25 km size.

Performance Evaluation of Water Control with Nanoemulsion as Pre-pad Fluid in Hydraulically Fracturing Tight Gas Formations

“…The experimental results indicated that water permeability dramatically declined, though gas permeability was slightly affected due to polymer adsorption on the pore surface . The traditional water shutoff agents including inorganic substances, polymers, or cross-linking agent–polymers for oil wells are found to impose a great negative impact on gas wells, especially for tight gas formations. − Subsequently, a modified polymer–cross-linking process was developed to not only induce gas channels within gel, but also re-establish gas permeability near the wellbore, selectively reducing water permeability . Another sequential gel/gas slug injection process was also proposed to perform water control in gas wells only in medium or high permeable porous media, which can significantly reduce the water–gas ratio .…”

Restriction of Water Production in Gas Wells by Induced Phase Inversion: Field Case Studies

“…Despite the serious arguments, polymer gels (and microgels) had been successfully applied under filed conditions in both vertical and horizontal wells (e.g. Wassmuth et al 6 , Zaitoun et al 7 , Al-Muntasheri et al 8 ) and inorganic gels were also reported to use in an Indonesian gas field by Cheneviére et al 9 . Having no doubts that sophisticated placement methods may lead to successful jobs, new ways should have been searched to develop more general techniques.…”