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Africa (Sub-Sahara) An 816-mile 2D seismic acquisition program was completed on the Ampasindava block, located in the Majunga deepwater basin offshore northwest Madagascar. The data will provide improved subsurface imaging of the large Sifaka prospect and will potentially mature additional prospects in the Ampasindava block to drill-ready status. Sterling Energy (UK) holds a 30% interest in the Ampasindava production sharing contract, which is operated by ExxonMobil Exploration and Production (Northern Madagascar) (70%). Asia Pacific Production began on the Liuhua 19-5 gas field in the Pearl River Mouth basin in the South China Sea. The field is expected to hit peak production of 29 MMcf/D this year. China National Offshore Oil Corporation (100%) is the operator. Drilling began on the YNG 3264 and the CHK 1177 development wells onshore in Myanmar.
Africa (Sub-Sahara) An 816-mile 2D seismic acquisition program was completed on the Ampasindava block, located in the Majunga deepwater basin offshore northwest Madagascar. The data will provide improved subsurface imaging of the large Sifaka prospect and will potentially mature additional prospects in the Ampasindava block to drill-ready status. Sterling Energy (UK) holds a 30% interest in the Ampasindava production sharing contract, which is operated by ExxonMobil Exploration and Production (Northern Madagascar) (70%). Asia Pacific The Jolly-1 well, located in the Otway basin onshore in South Australia, was spudded in petroleum exploration license (PEL) 495. The primary objective of the well, whose planned total depth is 4000 m, is to assess the unconventional oil and gas potential of shales within the Casterton formation. Beach Energy (70%) operates PEL 495, with partner Cooper Energy (30%). Production began on the Liuhua 19-5 gas field in the Pearl River Mouth basin in the South China Sea.
Reservoir compaction in depleting gas fields can cause seismicity, as has been observed in a dozen countries (Foulger
For a few gas reservoirs, the evolution of potential fault slippage is simulated using the commonly adopted Mohr-Coulomb failure criterion. This shows that fault criticality is expected for reservoirs that showed seismic as well as non-seismic behavior. Apparently, some characteristic property is missing to explain the difference in behavior.
Using published pressure histories for seismically active gas fields, the relation is shown between seismic magnitude and relative depletion. It appears that in many cases, the first induced earthquake is relatively strong which suggests substantial cohesion of the faults. It is plausible from the geological history that in non-seismic regions, fault cohesion is larger, so that slippage is inhibited.
Drilling hazards can lead to significant cost overruns during the drilling phase and might cause unsafe situations or potentially harm the environment. Often the local geology, when poorly understood, is the trigger of a drilling incident. By sharing past drilling experience and in particular observations on Geo-Drilling Hazards, via a suitable platform, well planning and risk assessment can be carried out more effectively. After analysing historic drilling reports, observations on drilling incidents have been compiled using a structured approach. Classification schemes allow systematic capture of key information in a format suitable for a database. In this process the observations (
The Geo-Drilling Events (GDE) database currently covers some 1000 boreholes from the Netherlands. Around 1400 geo-drilling events have been analysed systematically allowing to identify drilling hazard hotspots in a statistically meaningful sense. Examples of geo-drilling events include
Planned well trajectories can now be screened efficiently for geo-drilling hazards. The GDE Tool based on advanced classification criteria allows to share relevant well information across all operators active in the Netherlands. This includes newcomers, like geothermal operators who carry out a lot of drilling nowadays. The GDE Tool allows everyone to learn from the experience on drilling hazards gathered over the years by oil companies.
Weijermans, Peter-Jan (Neptune Energy Netherlands B.V.) | Huibregtse, Paul (Tellures Consult) | Arts, Rob (Neptune Energy Netherlands B.V.) | Benedictus, Tjirk (Neptune Energy Netherlands B.V.) | De Jong, Mat (Neptune Energy Netherlands B.V.) | Hazebelt, Wouter (Neptune Energy Netherlands B.V.) | Vernain-Perriot, Veronique (Neptune Energy Netherlands B.V.) | Van der Most, Michiel (Neptune Energy Netherlands B.V.)
The E17a-A gas field, located offshore The Netherlands in the Southern North Sea, started production in 2009 from Upper Carboniferous sandstones, initially from three wells. Since early production history of the field, the p/z plot extrapolation has consistently shown an apparent Gas Initially In Place (GIIP) which was more than 50% higher than the volumetric GIIP mapped. The origin of the pressure support (e.g. aquifer support, much higher GIIP than mapped) and overall behavior of the field were poorly understood.
An integrated modeling study was carried out to better understand the dynamics of this complex field, evaluate infill potential and optimize recovery. An initial history matching attempt with a simulation model based on a legacy static model highlighted the limitations of existing interpretations in terms of in-place volumes and connectivity. The structural interpretation of the field was revisited and a novel facies modeling methodology was developed. 3D training images, constructed from reservoir analogue and outcrop data integrated with deterministic reservoir body mapping, allowed successful application of Multi Point Statistics techniques to generate plausible reservoir body geometry, dimensions and connectivity.
Following a series of static-dynamic iterations, a satisfying history match was achieved which matches observed reservoir pressure data, flowing wellhead pressure data, water influx trends in the wells and RFT pressure profiles of two more recent production wells. The new facies modeling methodology, using outcrop analogue data as deterministic input, and a revised seismic interpretation were key improvements to the static model. Apart from resolving the magnitude of GIIP and aquifer pressure support, the reservoir characterization and simulation study provided valuable insights into the overall dynamics of the field – e.g. crossflows between compartments, water encroachment patterns and vertical communication. Based on the model a promising infill target was identified at an up-dip location in the west of the field which looked favorable in terms of increasing production and optimizing recovery. At the time of writing, the new well has just been drilled. Preliminary logging results of the well will be briefly discussed and compared to pre-drill predictions based on the results of the integrated reservoir characterization and simulation study.
The new facies modeling methodology presented is in principle applicable to a number of Carboniferous gas fields in the Southern North Sea. Application of this method can lead to improved understanding and optimized recovery. In addition, this case study demonstrates how truly integrated reservoir characterization and simulation can lead to a revision of an existing view of a field, improve understanding and unlock hidden potential.
The Slootdorp field has a complex structure with most reserves in Rotliegend sandstone, which is communicating with gas bearing Zechstein carbonates. The Rotliegend reservoir is bounded by a large fault, which might become seismogenic during depletion. A 3D geomechanical model was built, based on the faults and horizons in the geological model. Both the Rotliegend and Zechstein reservoirs were included in the model. The model was populated with geomechanical properties derived from logs, LOT's (leak off tests) and regional data on the stress field. Also, overburden properties from previous studies on nearby fields were used.
The pressure input was obtained from reservoir simulation. It is important to include the water leg pressure in the pressure input since the Rotliegend gas reservoir is in contact with an active aquifer. Pressure reduction drives the compaction of the reservoir, which induces stresses on the faults causing slippage. Since the water is quite incompressible, a large pressure reduction in the water leg may be caused temporarily by a rising gas water contact.
It turned out that slippage is not expected at the lowest gas pressure using a conservative estimate of the critical friction coefficient on the fault of 0.55. Sensitivity analysis on the most important input parameters was performed with a range that can be expected for such a field. The result was that the maximum critical stress ratio could range between 0.46 and 0.53 for the expected uncertainty of input parameters. The geomechanical modeling shows that an active aquifer has a dominant, mitigating effect on seismic risk, which can explain why many reservoirs show no seismicity in the Netherlands, although other effects could also play a role.
Well Placement encompasses the engineering and services required to spatially place all our well types in the optimal position with respect to current and future value creation. It is paramount that this placement firstly considers HSE with respect to existing wells, geohazards and our understanding of the pore-pressure/fracture gradient regime (well control). With this is mind Well Placement needs to apply a risk based multi-disciplinary approach. This session will cover the optimisation of survey acquisition and advanced quality control of existing systems, and also present the latest thinking with respect to trajectory definition and technology advancement.
Ruoff, Matthijs (Oranje-Nassau Energie B.V.) | Costa, Driss (Oranje-Nassau Energie B.V.) | Rosenberg, Steven (Weatherford) | Ameen, Sayamik (Weatherford) | Krol, Dariusz Krol (Weatherford) | Salomonsen, Halvard (Weatherford) | Tan, Ming Zo (Weatherford)
While drilling through the Permian Zechstein Group, North Sea operators can encounter a permeable overpressured interval which cannot be statically stabilized with conventional methods. An operator proposed drilling with Liner (DwL) in combination with managed pressure drilling (MPD) and continuous circulation technologies as a potential solution to this drilling hazard. In case that the overpressured interval was not seen, the DwL BHA could be retrieved after which the remaining section would be drilled conventionally. The DwL process allows a hazardous interval to be isolated in a single trip resulting in less risk and exposure compared with conventional drilling methods. Realizing the potential benefits automation brings, many operators have turned to MPD techniques as a technical and cost-rewarding solution to hard-to-reach assets, an approach which not only saves time but also enhances the safety capabilities of the operation. More importantly, MPD is increasingly being considered for other operations requiring precise pressure control to maintain wellbore integrity in constricted drilling envelopes. Continuous circulation technology provides a method to ensure continuous flow downhole while making connections which supplements the controlled annular pressure profile to avoid a drilling fluid / formation fluid change out. The prompt collaboration within the operator-service provider team determined which combination of these technologies would be the safest and most effective means for managing the overpressured interval should it be encountered.
This collaborative effort consisted of well engineering analysis and risk assessment sessions to ensure that the 12 ¼-in. hole objectives could be met in a safe and efficient manner aligning with the overall well objectives. The analyses included DwL, MPD, continuous circulation procedures and related simulation modelling for the running, drilling and cementation of the 9-5/8-in. × 13-3/8-in. liner. The combined technologies encompass a multitude of engineering disciplines; these were integrated into the operator's drilling plan in a seamless manner. Potential concerns and drilling hazards were identified and reduced to a manageable level. Ultimately, the 9-5/8-in. DwL system was used without encountering the overpressured interval and therefore the DwL BHA was retrieved with the remaining 12-1/4-in. hole interval conventionally drilled to planned depth without incidents. This paper will illustrate inclusion of DwL, MPD and continuous circulation technologies in the drilling plan as an effective solution for the mitigation of hazardous intervals. It will also reinforce the value of a close working relationship between operator and integrated service providers to eliminate uncertainties and provide sufficient risk mitigation to ensure that intended well objectives will be met.
The IADC and SPE are committed to delivering a balanced agenda around Diversity and Inclusion, to support member companies as they strive to address the gap in the Oil & Gas Sector. In 2019 the SPE/IADC International Drilling Conference and Exhibition in The Hague will host a session that allows delegates to explore the challenges facing the industry and hear firsthand, how it can be addressed. This initiative aims to build on the efforts already being undertaken at individual company levels to attract, develop and retain female staff - especially in technical and senior management roles, and to remove barriers that may currently hinder or discourage women from rising through the ranks into leadership roles. The aim is to address the factors contributing to the gender gap and to advantage all companies, their owners and shareholders through the incremental performance and value that parity will generate. This is good for our people, good for our stakeholders, and good for our business. Whilst in 2017 the session focused on subjects arising from DAVOS 2016 namely Leadership, Aspiration, goal setting, STEM, recruitment and retention, corporate culture and work life balance, the panel now feel it is time to move the conversation forward with some hard-hitting topics that affect the lives of many. Make sure you join us for this special session in The Hague.
A novel well concept to unlock reserves from mature gas fields in Northern Germany has been developed. This concept combines cemented completions with through-tubing coiled-tubing drilling to enable significant cost reductions using ultra slim hole drilling in sour gas bearing, Upper Permian Zechstein dolomite reservoirs.
Once gas reservoirs mature, drilling of conventional infill wells can quickly become economically unattractive. Often this leaves resources untouched and it limits the economic life span of a field. To improve the economics of infill drilling in deep and mature gas fields significant cost reductions are necessary. These cost reductions can be achieved by changing the proven, yet costly, casing scheme to an ultra slim hole well concept. Besides unfavorable economics another challenge while drilling with conventional technology in mature fields can be the reduced inflow performance caused by formation damage. This challenge can be overcome by under- or at-balanced drilling, which is enabled by through-tubing coiled-tubing drilling.
Despite improved efficiencies gained from knowledge by drilling many offset wells, the estimated gas volumes are not sufficient to justify drilling of new wells with the established and conventional well design. Therefore, the operator prepared an advanced ultra slim hole well concept. The casing shoe setting depths remained unchanged, however the hole sizes are reduced significantly. The openhole reservoir section is changed from 5.875-in to 2.5-in and this section is drilled with coiled-tubing and through the installed completion. The size of the completion is selected to be 3.5-in and it is cemented in a 4.125-in hole. In this application, the cemented 3.5-in completion eliminates an entire 7-in liner that would be necessary in the conventional casing scheme. The remainder of the ultra slim hole well is drilled with a 5-in drilling liner, a 7-in intermediate casing and a 9.625-in surface casing. This needs to be compared with the conventional casing scheme comprising of an 18.625-in surface casing, a 13.375-in intermediate casing, a 9.625-in production casing and a 7-in liner. The reduction in cost is estimated to be in the order of 40%.
The presented concept can enable significant cost reductions and by applying this ultra slim hole concept further infill drilling in mature gas fields can become more economically attractive. Moreover, formation damage can be overcome by underbalanced drilling, which is enabled by drilling through-tubing with coiled-tubing. The synergies created by combining cemented completions with coiled-tubing drilling are presented in this paper.