Success story of integrated subsurface study to deliver a successful infill drilling: Buntal-5 case study

Buntal is a mature gas field located in South Natuna Sea Block B PSC. The field was discovered by well Buntal-1 and delineated by appraisal well Buntal-2. The field consists of multi-stacked sandstone reservoirs, which were deposited under fluvial deltaic environment. The major Buntal reservoirs have been produced since 2004 from two subsea wells. Buntal-3 was producing from zones Beta-1 and Beta-2, while Buntal-4 was a horizontal well producing from Zone-1C. Both of those wells had loaded up prior to Buntal-5 drilling. This paper describes the details of a multidisciplinary approach taken for the proposal of Buntal-5 infill drilling. An integrated geological and geophysical study were carried out to quantify resources and uncertainties of the remaining thin unproduced zones. In total, there are 8 virgin zones as Buntal-5 initial target namely Beta-0, Zone-1A, Zone-1B, Zone-1D, Zone-1E, Zone-2B, Zone-3 and Zone-3A. Max-trough seismic amplitude was utilized to identify geological features across for each Buntal reservoir. The result was then combined with geological concept based on its depositional environment to justify a reasonably higher hydrocarbon volume which can not be estimated only by wells’ data. A reservoir simulation study was also carried out to not only to evaluate production potential from the virgin zones but also to capture upside potential from the produced zones. Simulation history matching result on Zone-1C revealed early water breakthrough experienced by Buntal-4 well due to water cresting phenomena which left significant gas reserves. This result added upside potential to Buntal-5 which initially only targeted marginal remaining unproduced zones. The well was drilled at the end of 2019 and proven to be a major success. Buntal-5 open hole logs data indicate thicker and better virgin zones reservoir quality as expected by integrated geological and geophysical study. Furthermore, significant remaining gas was encountered in Zone-1C with actual gas water contact was within the simulation result proving the water cresting theory, the zone itself add well’s gas-in-place by 30% on top of the unproduced zones’ gas-in-place.

3D PETROPHYSICS FOR HAWE: CASE STUDIES

Most conventional log interpretation technics use the radial model, which was developed for vertical wells and work well in them. But applying this model to horizontal wells can result in false conclusions. The reasons for this are property changes in vertical direction and different depth of investigation (DOI) of logging tools. DOI area probably can include a response from different layers with different properties. All of this complicates petrophysical modeling. The 3D approach for high angle well evaluation (HAWE) is forward modeling in 3D. For this modeling, it is necessary to identify the geological concept near the horizontal well section using multiscale data. The accuracy of modeling depends on the details of the accepted geological model based on the data of borehole images, logs, geosteering inversion, and seismic data. 3D modeling can be applied to improve the accuracy of reservoir characterization, well placement, and completion. The radial model is often useless for HAWE because LWD tools have different DOI and the invasion zone was not formed. But the difference between volumetric and azimuthal measurements is important for comprehensive interpretation because various formations have different properties in vertical directions. Resistivity tools have the biggest DOI. It is important to understand and be able to determine the reason for changes in log response: a change in the properties of the current layer or approaching the layers with other properties. For this, it is necessary to know the distance to the boundaries of formations with various properties and, therefore, to understand the geological structure of the discovered deposits, and such information on the scale of well logs can be obtained either by modeling or by using extra deep resistivity inversion (mapping). The largest amount of multidisciplinary information is needed for modeling purposes - from images and logs to mapping and seismic data. Case studies include successful examples from Western Siberia clastic formations. In frame of the cases, different tasks have been solved: developed geological concept, updated petrophysical properties for STOIIP and completion, and provided solutions during geosteering. Multiscale modeling, which includes seismic, geosteering mapping data, LWD, and imagers, has been used for all cases.

Delivering A Successful Acid Fracturing Job Through Integrated GGR Analysis and Stimulation Study, Case Study of A Tight Gas-Condensate Reservoir In Central Kalimantan, Indonesia

The biggest challenge for producing a tight (<0.1 mD) gas-condensate reservoir is its low deliverability. Therefore, it is important to consider well stimulation in the field development program. There are several types of stimulation, and one of the types which has the most impact is acid fracturing. However, thorough study needs to be carried out to ensure its compatibility with the specific reservoir condition. This paper will describe in detail how the geology, geophysics and reservoir (GGR) analysis and the stimulation study play its role to create a successful acid fracturing job in Indonesia, specifically in Central Kalimantan. The study begins with the understanding of reservoir geological concept and its characterization using multiple seismic attributes and core sedimentology. This geology and geophysical (G&G) analysis is further enhanced by performing dynamic analysis such as pressure transient analysis (PTA), rate transient analysis (RTA), and flowing material balance (FMB). Following this, feasibility of acid fracturing is assessed by performing the geomechanical analysis and acid solubility test. Moreover, the fracture geometry is also simulated to make sure the resulting fracture is able to penetrate the good reservoir quality. Then, performance projection using reservoir simulation is performed to quantify the expected incremental gain from the job. The geological concept differentiates this platform carbonate into six depositional elements, in which all of the production wells are located in the Reef Complex. It is further defined using the combination of seismic attributes, petrophysical analysis, and production performance, which are able to map the reservoir quality distribution. From the dynamic analysis, it shows that each well has massive connected gas initial in place (GIIP) with several wells are having poor facies nearby that act as the barrier. The study is followed by a stimulation study which shows that the reservoir has hard rock characteristics (Young Modulus up to 3.2 million psi) and high acid solubility (up to 95%), suitable for acid fracturing job. Simulated fracture geometry shows that it could penetrate nearby poor facies and achieve the good facies target. Then, the reservoir simulation also shows that significant production gain could be obtained from the job. Following up on the encouraging result of GGR & stimulation study, the first acid fracturing campaign in this field is sanctioned and performed safely & successfully. It delivers a very encouraging result in which one of the wells shows a productivity increase of up to 200%. Production forecast shows that post-fracturing well performance could sustain the plateau rate up to two and a half years and provide an addition of 25 BSCF of proved developed producing reserves. Material enough for increasing the field profitability and optimizing future development plans. This study shows that understanding the reservoir by doing integrated GGR analysis has significant benefit to reveal the upside potential of the field. Moreover, the excellent result on acid fracturing feasibility study and fracture design prior to the job ensures that it could be performed safely, successfully, and significantly increase the well productivity.

Using Isometric Logratio Transformations (ILR) to interpret enzyme leach geochemical surveys

Enzyme selective extractions (ESE) aids in the detection of mineral deposits at depths ranging from a few meters to 800 metres and sometimes more. This selective extraction technique was developed over the past 25 years and it has been utilized successfully to locate many types of mineral deposits. Ore bodies are indicated by a host of elements that are distributed into positive and negative patterns at surface, above and around the margins of mineral deposits. Trace elements become trapped at parts-per-billion and parts-per-trillion levels within amorphous oxide coatings on sand and silt grains in the soil or sediment in the near-surface environment. Selective extraction by Enzyme Leach of amorphous MnO within these coatings and subsequent analysis for up to 68 trace and major elements by ICP-Mass Spectrometry reveals repeatable patterns that indicate blind mineral bodies. One big advantage of this method is the simplicity of the sampling procedure and the small amount of material needed (10 g of the -60 Mesh fraction). Samples can be taken from any depth, although constancy in the depth of sampling is necessary. In the creation of the ILR matrix, the Author used the suite of elements provided by the ESE method (oxidation, base metals, chalcophile base metals, High Field Strength Elements (HFSE), Rare Earth Elements (REE), lithophile, Platinum Group Element (PGE), and Major Oxides suites). This provides the opportunity of introducing a geological concept into the actual processing of the data and the creation of a new sort of geochemical prospecting map- one that looks for deposit type instead for individual elements or their combinations. The method was applied to several datasets that allowed the detection of new targets in Armenia, Colombia, Chile, Mozambique, and elsewhere.

Foucault’s End of History: The Temporality of Governmentality and its End in the Anthropocene

Michel Foucault’s concept of governmentality is widely used throughout the social sciences to analyse the state, liberalism, and individual subjectivity. Surprisingly, what remains ignored are the repeated claims made by Foucault throughout his seminal Security, Territory, Population lectures (2007) that governmentality depends more fundamentally on a specific form of time, than on the state or the subject. By paying closer attention to Foucault’s comments on political temporality, this article reveals that governmentality emerged from, and depends upon, a very specific cosmological order that experiences time as indefinite: what Foucault calls our modern ‘indefinite governmentality’. This is elaborated here in three ways. First, by reviewing the transformation from a linear Christian cosmology to our modern indefinite governmentality through what Foucault calls the ‘de-governmentalization of the cosmos’. Second, by arguing that our experience of indefinite temporality was concretised by the geological discovery of ‘deep time’. Third, by engaging a contemporary geological concept that returns humanity to its lost cosmological centrality, thereby re-governing the cosmos: the Anthropocene, or the ‘human epoch’. Analysed using indefinite governmentality, Foucault’s forewarning of an ‘end of history’ is implicit in the new concept of the Anthropocene’s origins and ends. If it is the paradigm shift its proponents claim, then it threatens to end the temporality of the state, the subject, and governmentality itself.