Napalowski, Ralf (BHP Billiton) | Loro, Richard (BHP Billiton) | Anderson, Calan Jay (BHP Billiton) | Andresen, Christian Andre (ResMan AS) | Dyrli, Anne Dalager (ResMan AS) | Nyhavn, Fridtjof (ResMan AS)
This paper describes the interventionless approach that was successfully executed during the Pyrenees early production phase to identify the timing and location of water breakthrough. Chemical inflow tracers were installed in key production wells within the lower completion along the horizontal production sections. Results from this work have supported the reservoir simulation history matching process and confirmed the performance of the inflow control devices (ICDs). These data in conjunction with the real time rate information from subsea multiphase meters has allowed proactive reservoir and production management that has contributed to the early identification of additional infill opportunities.
Low matrix permeability and significant damage mechanisms are the main signatures of tight gas reservoirs. During drilling and fracturing of tight formations, the wellbore liquid invades the tight formation, increases liquid saturation around wellbore and eventually reduces permeability at near wellbore. The liquid invasion damage is mainly controlled by capillary pressure and relative permeability curves.
Water blocking and phase trapping damage is one of the main concerns in use of water based drilling fluid in tight gas reservoirs, since due to high critical water saturation, relative permeability effects and strong capillary pressure, tight formations are sensitive to water invasion damage. Therefore, use of oil based mud may be preferred in drilling or fracturing of tight formation. However invasion of oil filtrate into tight formations may result in introduction of an immiscible liquid hydrocarbon drilling or completion fluid around wellbore, causing entrapment of an additional third phase in the porous media that would exacerbate formation damage effects.
This study focuses on phase trapping damage caused by liquid invasion using water-based drilling fluid in comparison with use of oil-based drilling fluid in water sensitive tight gas sand reservoirs. Reservoir simulation approach is used to study the effect of relative permeability curves on phase trap damage, and results of laboratory experiments core flooding tests in a West Australian tight gas reservoir are shown in which the effect of water injection and oil injection on the damage of core permeability are studied. The results highlights benefits of using oil-based fluids in drilling and fracturing of tight gas reservoirs in term of reducing skin factor and improving well productivity.
Tight gas reservoirs normally have production problems due to very low matrix permeability and different damage mechanisms during well drilling, completion, stimulation and production (Dusseault, 1993). The low permeability gas reservoirs can be subject to different damage mechanisms such as mechanical damage to formation rock, plugging of natural fractures by invasion of mud solid particles, permeability reduction around wellbore as a result of filtrate invasion, clay swelling, liquid phase trapping, etc (Holditch, 1979).
In general, for tight sand gas reservoirs, average pore throat radius might be very small and therefore it may create tremendous amounts of capillary forces. Capillary forces cause the spontaneous imbibition of a wetting liquid (in this case water) in the porous medium in the absence of external forces such as a hydraulic gradient (Bennion and Brent, 2005). This causes significantly high critical water saturation (Bennion et al., 2006). Two forces drive capillary flow (Adamson and Gast, 1997). The first is the reduction in the surface free energy by the wetting of the hydrophilic surface (wettability). In hydraulic fracturing, water in the fracturing fluid wets the surface of the pores in the rock, resulting in a decrease in the surface free energy of the pores. The other force that drives capillary flow is the capillary pressure.
Tight gas reservoirs might be different in term of initial water saturation (Swi) compared with critical water saturation (Swc), depending on the geological time of gas migration to the reservoir. Initial water saturation might be normal, or in some cases sub-normal (Swi less than Swc) due to water phase vaporization into the gas phase (Bennion and Thomas, 1996). The initial water saturation might also be more than Swc if the hydrocarbon trap is created during or after the gas migration time. A sub-normal initial water saturation in tight gas reservoirs can provide higher relative permeability for the gas phase (effective permeability close to absolute permeability), and therefore relatively higher well productivity (Bennion and Brent, 2005).
Quinlan, Timothy Michael (Schlumberger) | Sibbit, Alan Matthew (Services Techniques Schlumberger) | Rose, David Alan (Schlumberger) | Brahmakulam, Jacob V. (Schlumberger) | Zhou, Tong (Schlumberger) | Fitzgerald, John Barry (Steve Kimminau Consulting) | Kimminau, Stephen John
Carbon Dioxide (CO2) sequestration and enhanced recovery projects require the evaluation of rocks containing mixtures of CO2, water, and gaseous or liquid hydrocarbons. Pulsed neutron logs of various designs and measurement types have been used since the 1960s to evaluate formations containing gaseous hydrocarbons, but they were not originally designed or characterized specifically for quantitative CO2evaluation. Computer modeling, test pit data, and field examples are presented in this work to highlight the issues of CO2 evaluation and to compare these with gaseous hydrocarbons.
Pulsed neutron tools emit 14 MeV neutrons from an accelerator source, but a wide variety of timing sequences, detector types, source-detector spacings, and signal processing techniques are employed by the industry to extract formation description parameters from the recorded counts. For the non-specialist petroleum engineer this variety can confuse and distract from effective use of the measurements. We organize all categories of pulsed neutron logs into simple types based upon the measurement physics to provide an effective guide to field use of these logs.
Examples of commercial and experimental tools in clastic and carbonate environments are presented. The examples show how CO2 can be quantified and demonstrate critical design requirements for successful pulsed neutron logging campaigns. We outline the lessons learned and make recommendations for the design of logging programs and interpretation of the acquired data in stand-alone or in time-lapse modes.
In May 2011 Shell announced its commitment to the development of a Floating Liquefied Natural Gas (FLNG) concept by taking the Financial Investment Decision on the Prelude FLNG Project. Prelude is located in Australian offshore waters, approximately 475 km north-northeast of Broome and 825 km west of Darwin, and will be Shell's and possibly the world's first FLNG development. FLNG offers a number of environmental advantages over traditional onshore LNG developments. This paper describes some of these and the associated environmental permitting/approval conditions for the project.
The water surrounding Barrow Island (BWI), Western Australia is an internationally significant marine protected area for coral and turtle conservation. A key commitment of the Gorgon Project is that no marine pests be introduced to island waters. A comprehensive quarantine strategy has been developed to prevent the introduction of marine pests, monitor for any that have penetrated the quarantine barriers, and respond to any introductions of such pests.
All vessels mobilising to Barrow Island must be free of secondary biofouling (barnacles, bryozoans, hydroids and worms) at the time of mobilisation. In meeting this criterion, all vessels undergo an initial risk assessment to determine the risk of being infected with marine pests and measures are taken to remediate or mitigate such risks. A preference exists to drydock vessels. In-water inspections and cleaning are also undertaken for vessels that remained in high risk areas following drydocking.
The key question "How long can vessels remain in-water and still be considered to be free of secondary biofouling??? is ecologically and economically significant. To address this, the results of 32 vessel inspections were analysed, including vessels commencing, ongoing and departing from Gorgon service. A range of vessels were considered: offshore support vessels, landing craft tankers, dredges, barges, utility vessels and crew transport vessels. The results have significant implications for all vessel owners that work in sensitive marine areas. It is also an important indication that the current risk assessment methods underestimate the risks vessels present to marine ecosystems, more so when vessels operate in marine protected areas.
To date, quarantine measures to prevent the introduction of marine pests to Barrow Island from overseas have been effective.
As part of the Devil Creek Development Project, Apache successfully used horizontal directional drilling (HDD) with a delayed break out as the installation method for the shoreline crossing of a new gas pipeline at Gnoorea Point, 45 km southwest of Dampier, Western Australia to achieve excellent environmental and social outcomes.
Technical, environmental and community engagement challenges included an HDD reach distance of 1.85 km, a delayed break out technique, hard complex and variable geological strata, the HDD exit point in shallow water (6 m) and surrounded by benthic habitats consisting of corals, seagrass and macroalgae within a Marine Conservation Reserve, stringent regulatory requirements and the onshore drilling location directly adjacent to a heavily used camping area and a public boat ramp with adjacent beach.
To achieve minimal disturbance to the marine environment and social amenity of the surroundings, an extensive and innovative marine monitoring programme was used in combination with an intensive community engagement programme. The techniques used for this project have application to oil and gas activities involving stringent regulatory requirements, sensitive marine environments and proximity to public amenities.
Results, Observations and Conclusions
Mapping of the drilling fluid showed a small area of the seabed that was affected. Some small, unplanned areas of leakage of drilling fluid onto the seabed were also identified and the leaks remediated: these leakages occupied only a very small area of the seabed. Apache were required to demonstrate that HDD activities resulted in no more than 0.5% loss of seagrass, macroalgae and coral based upon losses predicted from mapping, modeling suspended sediment concentrations in the water column and sedimentation rates on the seabed based on drilling fluid discharge rates and applying conservative coral health threshold criteria to discharge model outputs to predict zones of impact to benthic habitats. An extensive marine monitoring programme, sampling before and after HDD, using high definition video camera to capture photoquadrats conclusively demonstrated that losses were significantly less than predicted and permitted.
Drilling operations were a 24 hour activity and located directly adjacent to a popular camp site and boat ramp. Apache engaged with the community before and during the HDD activity and no complaints were received from the users of the area during operations.
Significance of the Subject Matter
Provides an example of industry's ability to operate successfully in sensitive marine environments and close proximity to communities.