Seismic, well data and regional geology indicate that the Top Gotnia salt was deposited on a broad carbonate platform. This sequence undergoes a lateral transition from halite to dominantly anhydrite in the southwest & southern Kuwait. Seismic facies analysis is carried out to map facies change and develop a depositional model for Gotnia Salt-1 (GS1), South Kuwait. A seismic line, which tied wells north to south was selected to analyze facies transition and processed for stratigraphic objective. The seismic interpretation procedure consisted of three steps: seismic sequence identification, seismic facies analysis, and Late Jurassic structural analysis in the Dibdibah Trough between Khurais-Burgan and Summan Archs. Seismic facies descriptions involving amplitude and continuity were confined to the GS1 sequence because of limited internal reflection detail. Detailed seismic characterization is carried by generating Acoustic Impedance (AI) volume and waveform classification map. Facies map based on these descriptions and reflection variation established the gradual transition of GS1 to dominantly anhydrite facies.
Late Jurassic Gotnia & Hith Formations (Fm.) in Kuwait were traditionally considered as regional seals for the underlying hydrocarbon bearing reservoirs of Najmah, Sargelu and Marrat. Recently, drilling of development well in north Kuwait has brought out a phenomenal change in the scenario bringing out the potential of a column of Gotnia and Hith as reservoir rocks. Comprehensive logging suites are rarely recorded through the Gotnia section due to extreme over-pressure related drilling issues within the zone. After judging the immense hydrocarbon potential of encased carbonate bands within anhydrite-1 unit of Gotnia in North Kuwait, Jurassic wells are being logged while drilling. Log interpretation indicates these thin carbonate bands encased in the Anhydrite layers (Hith-Gotnia), a sleeping giant play in Kuwait.
The location map (Figure 1) indexes the 2D seismic lines in the southwest and 3D seismic (Minagish-Umm-Gudair) in the southern Kuwait. While seismic horizon mapping of the top salt unit, the high amplitude and high continuity character of this reflector decrease noticeably in the south and southwestern part of the Kuwait, suggesting a change in depositional environment. Seismic data for top salt layer of the Gotnia section were not so far interpreted for unconventional objectives. Seismic facies analysis approach was chosen to map the limits of change in the GS1 facies.
Parmjit Singh, Riyasat Husain, Mafizar Rahaman, Anton Prakoso, Abdulaziz Al-Fares M., Kuwait Oil Company Abstract Modern exploration requires an integrated approach wherein disparate pieces of information from different disciplines need to be integrated toward the estimation of reservoir properties and facies of interest especially when the reservoir thickness is very thin. The final hydrocarbon production depends on the porosity, permeability, fluid saturation and the extent and thickness of the reservoir. The first step was to calibrate well data to the seismic attributes, namely amplitude and impedance. The cause of the very low Acoustic Impedance (AI) is analyzed with the fault attributes. The automatic seismic facies analysis is used to classify similar seismic traces based on amplitude, phase, frequency and other seismic attributes.
Perumalla, Satya (Baker Hughes Inc) | Al-Fares, Abdulaziz (Kuwait Oil Company) | Husain, Riyasat (Kuwait Oil Company) | Mulyono, Rinaldi (Kuwait Oil Company) | Al-Ammar, Nada (Kuwait Oil Company) | Al-Kandary, Ahmad (Kuwait Oil Company) | Singh, Hemant (Baker Hughes Inc) | Al-Naeimi, Reem (Baker Hughes Inc) | Prasad, Umesh (Baker Hughes Inc) | Scheele, Erik (Baker Hughes Inc) | Barton, Colleen (Baker Hughes Inc)
KOC has undertaken an initiative to generate a regional in situ stress map for 23 Kuwait oil and gas fields using the data from more than 400 wells. Key objectives of this project are to integrate all available well data sources from these fields to derive the in situ stress orientation and also to create an interactive digital stress map supported by sub-surface structural geological data including formation seismic horizons, faults and well markers with the help of visualization software. In this way, the outcome of this project is available as an interactive geomechanical knowledge base which can be viewed at regional scale.
The results of this project indicate that the maximum principal stress azimuth in Cretaceous formations is consistent with the regional Zagros tectonics and it is more or less uniform N45° (±10°) E direction even across major fault systems. However the sub-salt Jurassic formations exhibit high variability in stress orientation across faults as well as in the vicinity of fracture corridors. In addition to the patterns seen in stress orientation, the geomechanical models from each field exhibited that the Gotnia Salt is mechanically decoupling the highly stressed, strong, Jurassic formations from shallower, relatively lower stressed and weaker Cretaceous formations. It was also found that these stress anomalies in Jurassic formations coincide with associated fault and fracture corridors which appear to be critically stressed. Characterizing critically stressed fractures at the wellbore scale provided an understanding of possible permeable fracture sets that could contribute to gas flow.
This paper discusses detailed results of the regional stress distribution patterns including innovative criteria developed to manage quality control of stress orientation data, correlation between stress anomalies and structural geological elements in Kuwait and also covers insights developed for exploration and development strategies of deep gas reservoirs in Kuwait.
Introduction and Objectives
Mapping of sub-surface structures and in situ reservoir properties have been in practice by explorationists for more than a century. The structural maps and profiles provide understanding of geological history and conditions that are essential for play evaluation. Many conventional oil & gas fields in the world have been explored and developed and many are at a mature state. However, limited data are available to map the present day in situ stresses in these fields, as typical conventional exploration techniques assume theoretical stress estimations based on a regional understanding of tectonic history related to the evolution of a particular field structure. Occasionally, seismic attributes have been used to complement these geological estimates. Consequently, there has been little appreciation of the influence of in situ stresses on exploration and development strategies. More recently, it has been realized that geomechanics plays a key role in various ways from exploration through field development including wellbore stability analysis (for improved drilling experience) to reservoir geomechanical analysis (for optimization of production).
To understand the geophysical responses of shale oil/gas plays for identifying sweet spots, we use a rock physics relationship for calculating total organic carbon (TOC) from the Bulk density log (RHOB) and the ΔlogR separation techniques. The TOC values based on core/cuttings samples of wells are in the range of 7-10% and similar values are computed from the well log responses. Elastic properties of TOC-rich shale formation for computation of Young’s modulus (YM), Poisson’s ratio (PR) and brittleness from well-log-derived Vp,Vs and bulk density to understand the competency of the shale rock to frac for stimulation of reservoir. Average of absolute amplitude was extracted from P-impedance volume of 3D seismic data within the mapped “Hot Shale” pack to understand the relationship between acoustic impedance (AI) and the TOC at well locations and thus, use this analogy away from the structures in the basinal area. The impedance calculated directly from the relevant logs was cross checked with that extracted from the impedance volume. The low AI areas directly indicate high porosity rock which may be rich in kerogen identified as sweet spots.
The low exploration cost and abundance of occurrence had made conventional hydrocarbon resources very attractive, with depletion of these resources effort has shifted to the unconventional resources; shale is one such important resource. The growth of production from shale resources in last decade, particularly from the USA; is an indicator that these resources are likely to be a major contributor to energy needs of the mankind. A preliminary study was done in onshore part of the State of Kuwait to assess the potential of shale resources. There are two major shale sequences that are established sources of the hydrocarbons in the State of Kuwait, Najmah Shale at Jurassic level and Basal Makhul Shale at Cretaceous level. The major play elements for shale gas exploration have been studied as a pre-cursor to increased exploratory activity. These shale sequences have good potential for exploration and subsequent exploitation. This study is restricted to ‘Makhul Shale’ with emphasis on how best the seismic data can be used to augment the well data for exploration of this unit, unconventional method of blending more than one attribute has been used for detection of faults. The shale exploration in the State of Kuwait is in infancy and some efforts have started to understand it with limited data availability.
Gomez, Ernest (Schlumberger) | Al-Faresi, Fahad A. Rahman (Kuwait Oil Company) | Belobraydic, Matthew Louis (Schlumberger) | Yaser, Muhammad (Schlumberger) | Gurpinar, Omer M. (Schlumberger) | Wang, James Tak Ming (Schlumberger) | Husain, Riyasat (Kuwait Oil Company) | Clark, William (Schlumberger) | Al-Sahlan, Ghaida Abdullah (Kuwait Oil Company) | Datta, Kalyanbrata (KOC) | Mudavakkat, Anandan (KOC) | Bond, Deryck John (Kuwait Oil Company) | Crittenden, Stephen J. (KOC) | Iwere, Fabian Oritsebemigho (Schlumberger) | Hayat, Laila (KOC) | Prakash, Anand (KOC)
The Burgan Minagish reservoir in the Greater Burgan Field is one of several reservoirs producing from the Minagish formation in Kuwait and the Divided Zone. The reservoir has been produced intermittently since the 1960s under natural depletion. A powered water-flood is currently being planned. The pressure performance of the reservoir has proved hard to explain without invoking communication with other reservoirs. Such communication could be either with other reservoirs through the regional aquifer of through faults to other reservoirs in the Greater Burgan field. Recent pressures are close to the bubble point.
A coarse simulation model of the nearby fields and the regional aquifer was constructed based on data from the fields and regional geological understanding. This model could be history matched to allow all regional pressure data to be broadly matched, a result which supports the view that communication is through the regional aquifer. Using this model to predict future pressure performance suggested that injecting at rates that exceeded voidage replacement by about 50 Mbd could keep reservoir pressure above bubble point. It was recognized that the process of history matching performance was non-unique. This is a particular concern in the context of this study because the model inputs that were varied in the history matching process included aquifer data that was very poorly constrained. To address this problem multiple history matched models were created using an assisted history matching tool. Using prediction results from the range of models has increased our confidence that a modest degree of over-injection can help maintain reservoir pressure.
This paper demonstrates the utility of computer assisted history match tools in allowing an assessment of uncertainty in a case where non-uniqueness was a particular problem. It also emphasizes the importance of understanding aquifer communication when relatively closely spaced fields are being developed.