Richard, Pascal (Shell Global Solutions International BV) | Lamine, Sadok (Shell Global Solutions International BV) | Pattnaik, Chinmaya (Kuwait Oil Company) | Al Ajmi, Neama (Kuwait Oil Company) | Kidambi, Vijay (Kuwait Oil Company) | Narhari, Rao (Kuwait Oil Company) | LeVarlet, Xavier (Shell Kuwait Exploration And Production BV) | Swaby, Peter (Swaby Software Limited) | Dashti, Qasem (Kuwait Oil Company)
The North Kuwait Carbonate (NKJG) reservoirs are currently under development by KOC (Kuwait Oil Company). The appraisal and development of the NKJG offer challenges such as lateral variations in reservoir quality, tight to very tight reservoirs and natural fracturing to a varying degree spatially. The presence of open, connected fractures is one of the key elements to achieve a successful development. Also, the presence of fracture corridors increase the risk associated with drilling. Numerous fracture modelling studies have been supporting both appraisal and development strategies of the fields.
A structural evolution model has been developed based on field observations and linked to the regional phases of deformations. Detailed fracture characterization using static BHI (bore hole images) and core data as well as dynamic data has been achieved. Small scale detailed DFN (Discrete Fracture Network) in support of planning and drilling activities of future appraisal wells has been carried out. Full field DFN in support to production history matching and forecast has been completed. The core and pressure transient analysis data have been used to calibrate the permeability and porosity of the DFN property ahead of the dynamic simulation work.
This paper illustrates some examples of best practices of the various study components with a focus on core to BHI calibration, fracture porosity calibration using core data and calibration of DFN models using pressure transient analysis data.
Richard, Pascal (Shell Project and Technology) | Lamine, Sadok (Shell Project and Technology) | Pattnaik, Chinmaya (Kuwait Oil Company) | Kidambi, Vijaya (Kuwait Oil Company) | Narhari, Srinivasa (Kuwait Oil Company) | Al-Ajmi, Neama Hussain Abdullah (Kuwait Oil Company) | Dashti, X. Qasem (Kuwait Oil Company) | Varlet, Xavier Le (Shell Kuwait Exploration and Production)
Summary Seismic attribute data linked to main fault families interpreted from seismic and structural geology understanding has been used to constrain full field Discrete Fracture Network (DFN) Models. Pressure transient analysis data have also been used to further constrain the DFN models. The seismic attributes have also been combined with horizon curvature to create notional fracture sweet spot maps currently used to support well placement. The DFN models are now being used as input to production history matching and forecast generation. Introduction The North Kuwait Carbonate Gas (NKCG) reservoirs are currently under development by KOC (Kuwait Oil Company).
Pattnaik, Chinmaya (FDGS, Kuwait Oil Company) | Rao, Narhari Srinivasa (FDGS, Kuwait Oil Company) | Al-Ashwak, Samar (FDGS, Kuwait Oil Company) | Al-Ajmi, Neema Hussain (FDGS, Kuwait Oil Company) | Kidambi, Vijaya Kumar (FDGS, Kuwait Oil Company) | Al Anzi, Abdullah Motar (FDGS, Kuwait Oil Company) | Dashti, Qasem (FDGS, Kuwait Oil Company) | Staffelbach, C. (Corias) | Barbé, Jean-françois (Corias)
Fracture characterization is vital for efficient field development of naturally fractured Carbonate reservoirs. Successful development of fracture reservoir in the study area was possible due to early recognition of fracture play right from the exploration phase and through careful execution of relevant data acquisition campaign in the initial stages of field development. Comprehensive and integrated studies have been carried out over the past few years to arrive at an understanding of the conceptual model in deciphering structural evolution of North Kuwait Jurassic.
Extensive core and image log data was acquired in the initial stages of field appraisal, which helped in comprehensive forward planning in design of deviated and horizontal wells. The data analysis steps included accurate and reliable reorientation of the cores. These data were calibrated with the image logs, along with available seismic attributes, which resulted in better understanding of structural evolution and sweet spotting of horizontal wells. This reorientation of the core data also helped in establishing a number of quantitative fractures attributes such as frequency, spacing, dip-azimuth and aperture along with mapping of in-situ stress directions. The detailed integration of these data also helped in accurately mapping the local and regional present day stress and its variations spatially across the fields. Stress direction across the field was helpful for deciding the azimuth of wells during well planning along with selection of completion strategy for current set of horizontal drilling Campaign.
Drilling and testing results have been encouraging through enhanced reservoir performance in these tight carbonate reservoirs, based on these integrated studies.
Al-Ajmi, Saad A. (Kuwait Oil Company) | Pattnaik, Chinmaya (Kuwait Oil Company) | Al-Dawood, Ahmed E. (Kuwait Oil Company) | Dashti, Qasem (Kuwait Oil Company) | AlFailakawi, Abdul Aziz H. (Kuwait Oil Company) | Chakravorty, Sandeep (Schlumberger Oilfield Eastern Limited) | Chandan, J. Keot (Schlumberger Oilfield Eastern Limited) | El-Derini, Khaled M. (Schlumberger Oilfield Eastern Limited)
Kuwait Oil Company is currently engaged in an early phase development of deep sub-salt tight naturally fractured carbonate reservoirs. These reservoirs has been tested and found to be gas bearing. They are uniquely characterized by dual porosity nature where natural fracture network systems are the primary flowing mechanism. The foremost challenge to produce from these reservoirs is the wellbore interaction with the natural fracture network systems. Despite drilling around 85 vertical and slightly deviated wells in this large challenging HP/HT reservoir complex, understanding and characterization of fractures is a challenge in the absence of horizontal wells, though fracture understanding has improved over time through careful integration and interpretation of logs, core, and seismic data. To achieve the dual objective of characterizing the fractures and to boost production, asset team recently embarked on the strategy to drill horizontal wells targeting these challenging tight reservoirs. As a fit for purpose solution to address these challenges, "High Definition Deep Directional Multi Boundary Detecting Technology" was incorporated in the drilling plan so that horizontal producers could be geosteered in the desired target intersecting as much fractures as possible. This technology, an advancement on the 1st generation "Distance to Boundary" technology is characterized by its extended capability to detect multiple bed boundaries based on resistivity contrast up to 20ft around the wellbore. The significantly improved new multilayer stochastic inversion also solves for structural dip along the wellbore azimuth (longitudinal dip). In the lateral section, this technology successfully mapped the reservoir roof as well as multiple thin intra layers inside the target reservoir along with information on longitudinal dips which helped immensely to optimize trajectory inclination and spatially position the wellbore across different layers as per plan. Apart from detecting reservoir boundaries, the inversion also mapped conductive and resistive fractures cutting wellbore at high angle for the first time, while trajectory was drilling across a fracture corridor. This further added confidence to geo-steering while drilling as wellbore cutting through such a fracture corridor was highly anticipated in predrill planning. Drillpipe conveyed borehole images acquired after drilling the well confirmed the presence of large swarms of fractures detected through inversion.
The effective integration of data from different fields in a single platform, like LWD logs, boundary information, dip information, drill cuttings information and decisions taken based on the interpreted information paved the way for the successful drilling of this well and achieve the predrill objectives.
Richard, Pascal (Shell International) | Bazalgette, Loic (Petroleum Develoment Oman) | Kidambi, Vijaya Kumar (Kuwait Oil Company) | Laiq, Kamran (Schlumberger) | Odreman, Allan (Kuwait oil Company) | Al Qadeeri, Bashar (Kuwait oil Company) | Narhari, Rao (Kuwait Oil Company) | Pattnaik, Chinmaya (Kuwait Oil Company) | Al Ateeqi, Khalid (Kuwait Oil Company)
This paper presents a new structural model for the North Kuwait Carbonate fields as well as its implications in term of fracture modelling and field development. It also describes a workflow which can be used as foundation for further fracture modelling study at production and exploration scales alike. This workflow consists of a four step approach: 1) elaboration of a regional structural model, 2) creation of 3D conceptual fracture diagrams, 3) elaboration of constraints capturing the key elements of the conceptual diagrams and 4) creation of fracture model properties for further dynamic simulation.
The application of this workflow resulted in the creation of a series of fracture models for the North Kuwait Carbonates fields. During the first step of the study, a new structural model has been elaborated based on key kinematic observations from well and seismic data, as well as experimental and field analogues which have been linked to the known regional phases of deformation. These main phases of deformation are 1) post Triassic rifting, 2) Alpine 1 - late Cretaceous transtension and 3) Alpine 2 - Mid Tertiary compression related to the Zagros formation, which has the greatest impact on the formation of the pre-Gotnia structures and fracture development. The major difference between the new model and previous structural thinking is that the formation of the compressional folds in the Carbonate fields (an event that shaped the current outline of the fields) has happened during the Tertiary time instead of Jurassic time. The proposed structural evolution has been used to define characteristic structural domains. These structural domains have defined a foundation to elaborate conceptual fracture diagram to support fracture modelling study work. The fracture conceptual models have potential implications on fracture development and preferred direction of horizontal and deviated wells. Greater fracture connectivity is expected in compressional ridges developed in Tertiary time, while in the area between the compressional ridges, less dense fractures and probably more cemented fractures (likely to have developed before hydrocarbon emplacement ) are expected. The new view on the timing of the structural development (i.e., late uplift of compressional ridges regionally) also has possible implications on maturation/charge history as well as reservoir properties development.
The new proposed model for structural evolution is now being used as a foundation for appraisal and fracture modelling activities of the pre-Gotnia carbonate reservoirs. A fracture characterisation study integrating all available static and dynamic data is ongoing.
Kuwait Oil Company (KOC) is currently engaged in aggressively developing the challenging tight carbonate reservoirs (Figure 1) of North Kuwait spread over an area of approximately 1700 sq.km. A paradigm shift in field development process was adopted for tackling these hitherto less developed plays. These North Kuwait reservoirs are characterized by low porosity (average < 5pu), low permeability (average <0.1mD) and occur in deep (> 13500ft depth), HP/HT (average 11000psi/280°F) sour conditions. Though dolomitization improves reservoir characteristics in parts of the area, natural fractures play a dominant role in aiding production from these reservoirs. Hydrocarbon fluids in these reservoirs range from near critical gas-condensate to volatile oil. A detailed interpretation and integration of log, core, and seismic data helped in refining the depositional model. Due to the early life cycle stage of these fields, concurrent appraisal and development of all the fields is ongoing, and a phased development plan has been adopted by KOC as the appropriate development strategy. This allowed KOC to focus on the initial objectives of early assessment of potential in Phase I and to integrate the learning's from Phase I in to the subsequent development phases. The plan generated a strong technical case supporting the business decision to implement Phase II of the development. Currently wells are producing to an early production facility but the desired production capacity (Phase II) requires a large number of new wells to be drilled including horizontal wells.
Alenezi, Abdullah Matar (Kuwait Oil Company) | Narhari, Srinivasa Rao (Kuwait Oil Company) | Alajmi, Neema (Kuwait Oil Company) | Pattnaik, Chinmaya (Kuwait Oil Company) | Rao, Jonna Dayakar (Kuwait Oil Company) | Al-ateeqi, Khalid Abdullatif (Kuwait Oil Company) | Saffelbach, Christian (CORIAS) | Aris, Abdel-Hamid (Corpro Systems Ltd.) | Chakravorty, Sandeep (Schlumberger)
Natural fractures play main role in producibility of these reservoirs. An improved understanding of the fracture system may help to explain well behavior and could help in evaluation of reservoir properties. Application of seismic attributes along with core reorientation work has significant value addition in indicating areas of potential high fracture densities, assisting the well placement process in this purely fracture driven play. A better understanding of the fracture spatial orientation and fracture properties in the fields has a strong influence on further development plans of the fields in the studied area. 2 SPE 167301-MS Cemented and closed fractures act as barriers to flow, whereas open fractures intersected by the wellbore may increase the flow rates or result in early water breakthrough. Open fracture networks can cause some losses during drilling.
Chakraborty, Subrata Kumar (Schlumberger Oilfield Eastern Limited) | Rao, Narhari Srinivasa (Kuwait Oil Company) | Al-ajmi, Neema Hussain (Kuwait Oil Company) | Al-Ashwak, Samar (Kuwit Oil Company) | Kidambi, Vijay Kumar (Kuwait Oil Company) | Pattnaik, Chinmaya (Kuwait Oil Company) | Stelzer, Hermann (Schlumberger Oilfield Services)
Al-Eidan, Ahmad Jaber (Kuwait Oil Company) | Rao, Narhari Srinivasa (Kuwait Oil Company) | Al-Awadi, Mishari Ameen (Kuwait Oil Company) | Al-Ajmi, Neema Hussain (Kuwait Oil Company) | Pattnaik, Chinmaya (Kuwait Oil Company) | Al-Ateeqi, Khalid Abdullatif (Kuwait Oil Company) | Al-Houli, Maryam Mohammed (Kuwait Oil Company) | Kidambi, Vijay Kumar (Technically Write Consultants LL) | Dekeyser, Thomas
Exploration activity during the last eight years, targeting Jurassic carbonate reservoirs in North Kuwait, has culminated in the discovery of six major tight gas fields, encompassing an area of about 1,800 sq km with a reservoir gross thickness of about 2,200 ft. These fields are the first free-gas fields in Kuwait, which were put on early production during 2008. The reservoirs are characterized by dual porosity, dominated by low porosity and permeability, in deep HP/HT conditions, with wide variety of hydrocarbon fluids ranging from black oil to gas condensate with sour gas. Typical per well production rates are up to 5,000 BOPD/BCPD and 10 MMSCFPD, making them an excellent commercial success.
Despite the limited number of 38 well penetrations to date in this large Jurassic complex, understanding of the depositional model has improved over time through careful integration and detailed interpretation of log, core, and seismic data. Based on these studies, a depositional model incorporating sabkha, tidal flats, lagoon, backshoal, shoal, shoreface inner shelf, outer shelf, and slope/basin depositional environments has been built. Hypersaline brines were generated in the lagoon and seeped downward, selectively dolomitizing the underlying strata, creating secondary porosity and permeability, and significantly improving the reservoir characteristics in some of these fields. From the early phases of exploration, the role of natural fractures in enhancing the production from these reservoirs was recognized. Accordingly, well data acquisition is designed to maximize reservoir understanding. Delineation and development well placement are optimized to penetrate the most heavily fractured corridors, through a combination of seismic attributes and Discrete Fracture Network modeling, constrained by available well data.
Introduction and Historical background
Majority of wells in Kuwait are targeted for shallow Cretaceous reservoirs for conventional oil through fields discovered during the pre-70s (Fig.1). The exploration for deep Jurassic play was impacted due to lack of conventional reservoirs; particularly in the North Kuwait areas and very few deep wells were drilled targeting Jurassic reservoirs (Fig. 2). During the 90s' country wide coverage of 2D and 3D seismic data acquisition was carried out (Fig. 3). Detailed mapping and geo-scientific studies were undertaken utilizing these data sets (Fig 4). These studies resulted in a Paradigm shift in Play concept from conventional reservoirs to search for fracture plays during the late 90s' and early 2000. The focused exploration for fractured tight carbonate Jurassic reservoirs in the ensuing years resulted in the discovery of commercial quantities of oil and gas in the six fields Sabriyah, Raudhatain, Bahra, Northwest Raudhatain, Umm Niqqa and Dhabi in the North Kuwait area encompassing approximately 1800 sq.km. (Fig. 5)
Rao, Narhari Srinivasa (Kuwait Oil Company) | Al-Kandari, Abdullatif Y.A.M. (Kuwait Oil Company) | Kidambi, Vijay Kumar (Kuwait Oil Company) | Al-Ashwak, Samar (Kuwait Oil Company) | Al-Qadeeri, Bashar (Kuwait Oil Company) | Pattnaik, Chinmaya (Kuwait Oil Company)
Understanding fracture corridors is the primary driver for successful development of fractured carbonate reservoirs. This assumes further significance if the carbonate reservoir is characterized by very low porosity and permeability; producibility of the reservoir is purely dependent on the presence of natural fractures. Distribution and type of natural fractures is a function of palaeo & present day stress, structural elements, regional tectonics and diagenetic history. Direct detection of fractures is below the resolution of conventional seismic data. However, through a combination of seismic derived attributes integrated with well data, it is possible to better understand the distribution of fracture swarms.
Kuwait Oil Company (KOC) is currently engaged in an early phase of development of a tight fractured carbonate North Kuwait Jurassic gas play. Considering the limited well control, field development is heavily reliant on seismic data for fracture characterization. This paper presents our current understanding of the relationship between fractures observed in the well data and structures, faults and lineaments interpreted on seismic data. In addition to conventional seismic analysis a suite of seismic attributes including Dip, Coherence, Edge and 3D Volume curvature were used for mapping structures, faults and minor lineaments. Well-wise and field-wise analysis of relationships between seismic derived attribute-pattern and fracture orientation was established. The understanding between these two different sets of data has helped in locating potential zones of sweet spots for placing successful delineation and development wells. These seismic attribute volumes were also used as soft constraint for building the Discrete Fracture Network (DFN) model for populating the fracture network in the reservoir model. The data presented in this paper are from the Raudhatain, Sabriyah and North West Raudhatain (NWRA) fields for the Najmah-Sarjelu part of the Jurassic section.
Narhari, Srinivasa Rao (Kuwait Oil Company) | Al-Kandari, Abdul Latif (Kuwait Oil Company) | Kidambi, Vijaya Kumar (Kuwait Oil Company) | Al-Ashwak, Samar (Kuwait Oil Company) | Al-Qadeeri, Bashar (Kuwait Oil Company) | Pattnaik, Chinmaya (Kuwait Oil Company)