Implementation of Slurry Fracture Injection Technology for E&P Wastes at Duri Oilfield

Abstract

Abstract The Duri oilfield is one of the 141 oil fields operated in Sumatra, Indonesia by PT Caltex Pacific Indonesia under a production sharing contract with the Government of Indonesia.Discovered in 1941, the Duri field is one of the world's giant oilfields and the biggest steamflood operation located in the Rokan block with current oil production of 200,000 bpd (31,000 m3 per day).The insitu formations of the Duri field are unconsolidated sands; coupled with a steam flood operation they are susceptible to producing large quantities of oily viscous fluids as a by-product from the oil production. Up to 400 m3/day (2,500 bpd) of oily viscous fluids are generated at five oil production Central Gathering Stations (CGS) in the Duri oilfield. Slurry Fracture Injection™ (SFI™) is an environmentally viable deep well disposal process for Exploration and Production (E&P) waste streams. The SFI process can be used in the petroleum industry to dispose of produced solids, oily viscous fluids/sludges, tank bottoms, contaminated soils and drill cuttings. There are a number of environmental advantages associated with the SFI process that make it suitable for E&P waste management strategies that include: permanent disposal of waste materials, zero surface discharge, no adverse interaction with the environment, reduced risk of ground water contamination, and relatively low cost.The SFI process was determined to be the most environmentally viable process for E&P waste management at the Duri oilfield in Sumatra. This SFI project represents the first time that the SFI process was implemented in Indonesia. This paper details the SFI project assessment, development, and field operations related to this deep well disposal process at Duri. Introduction PT Caltex Pacific Indonesia (CPI) explored several alternative technologies to replace the surface-based processes used for E&P waste management at the Duri Steam Flood (DSF) oilfied in Sumatra (Figures 1).CPI undertook this study to ensure it employs environmentally sound waste management practices for E&P waste volumes generated at its Duri production operations. After considering several waste management options, CPI decided to use the Slurry Fracture Injection (SFI) process to dispose of E&P waste at the DSF, as this technology is a permanent disposal option at a relatively low cost, and is compliant with zero surface discharge criterion. The SFI process has been used in US and Canada and has been proven to be environmentally acceptable. The Slurry Fracture Injection - SFI process at the DSF is used for the disposal of oily viscous fluid waste streams. The waste material is screened to pass specified injection criteria. These wastes are then mixed with water to produce a pumpable slurry (for the purpose of this paper, the term ‘waste’ is defined to be any material prior to slurrification and disposal; the term ‘slurry’ is defined to be the waste material that has been blended with mix-water into a slurry stream).The slurry is made with as high a waste concentration as possible, typically 10–33% by volume.Deep disposal wells are used to inject the slurry under pressure into a suitable geological ‘target’ formation deep within the earth.Injection pressures are in excess of the fracture gradient of the disposal formation.The target formation(s) are high permeability, thick, unconsolidated sands. SFI operations at Duri are conducted on a daily basis (>8 hours/day, continuous injection cycles (> 48 hours/cycle, one cycle 3 days), and long term (12–15 days/month). Under such conditions, as waste material is injected into a formation, an area around the wellbore begins to fill with the injected waste material. The water component of the slurry dissipates into the formation. This waste filling area coalesces and evolves into a ‘waste pod’ (Figure 2). Relatively lower permeability, lower compressibility, and lower porosity than the surrounding formation can characterize this waste pod. The SFI process incorporates a number of unique monitoring and operating features that allow for effective process control during injection-disposal operations.Process control during SFI operations refers to: a) maintaining optimum formation injectivity; b) maintaining fracture containment; and c) maximizing formation storage capacity.With effective process control the SFI process is a permanent and environmentally sound disposal technique suitable for a variety of waste streams (Figure 2).