Wellbore instability is caused by the radical change in the mechanical strength as well as chemical and physical alterations when exposed to drilling fluids. A set of unexpected events associated with wellbore instability in shales account for more than 10% of drilling cost, which is estimated to one billion dollars per annum. Understanding shale-drilling fluid interaction plays a key role in minimizing drilling problems in unconventional resources. The need for efficient inhibitive drilling fluid system for drilling operations in unconventional resources is growing. This study analyzes different drilling fluid systems and their compatibility in unconventional drilling to improve wellbore stability.
A set of inhibitive drilling muds including cesium formate, potassium formate, and diesel-based mud were tested on shale samples with drilling concerns due to high-clay content. An innovative high-pressure high temperature (HPHT) drilling simulator set-up was used to test the mud systems. The results from the test provides reliable data that will be used to capture more effective drilling fluid systems for treating reactive shales and optimizing unconventional drilling.
This paper describes the use of an innovative drilling simulator for testing inhibitive mud systems for reactive shale. The effectiveness of inhibitive muds in high-clay shale was investigated. Their impact on a combination of problems, such high torque and drag, high friction factor, and lubricity was also assessed. Finally, the paper evaluates the sealing ability of some designed lost circulation material (LCM) muds in a high pressure high temperature environment.
An Under Balanced Drilling (UBD) pilot project in the Heera and Mumbai High fields of Western offshore India was recently completed successfully. The objective of the project was to establish whether the technology can improve productivity performance in the reservoir section, avoid reservoir damage and thereby enhance oil production from the wells. This paper incorporates the drilling experiences and challenges faced during execution of this pilot project, the well design considerations and methodology, evaluation of the drilling fluid systems and also describes the tangible benefits of using this technology in the drilling of these sections and wells. In terms of the productivity gains from drilling these wells using UBD technology, through the sub-hydrostatic formations offshore Mumbai, the results were very positive. With the success and encouraging results from the pilot project, more wells are now planned, including wells in the losses-prone and depleted Mumbai High and Neelam fields, to incorporate the experiences of the learning curve.
The paper discusses a petrophysical evaluation method for complex tight gas formations in a mature and partially depleted gas condensate field in Oman, allowing a full petrophyscial evaluation as well as geomechanical modeling from a source-less petrophysical dataset, thus reducing operational data acquisition risk in partially depleted reservoirs without compromising on hydraulic fracturing design. The developed methodology includes the volume of shale estimation from correlation with Poisson's ratio for the feldspathic rich tight formation. This methodology was used in deep tight fields in Oman for more than 3 years in both vertical and highly deviated wells greatly reducing the risk, logging cost and complexity of operations.
Oil and gas exploration in the deep-water areas have become a global hot spot. The deep-water area of the Baiyun sag in the Pearl River Mouth Basin is an important exploration target. The area is a typical deep-water hot basin of a wide range of geothermal gradients. Data from a single borehole shows a geothermal gradient from 4.0 to 6.64°C/100m. High geothermal field has an important control on the reservoir diagenesis, pore evolution and porosity-permeability trends. We analyzed sandstone samples from the ZhuJiang and ZhuHai Group, which were buried in the depth range between 500- and 4000m, and display similar composition and textures. The samples can provide insights into the evolution of reservoir diagenetic features under progressive burial process. We also analyzed sandstone samples frome EnPing Group. In general, the petrological composition was the main controlling factor of reservoir quality. The high geothermal field led to a rapid decrease in the porosity and permeability of deeply buried sandstones. Howerver, the EnPing Group, which has a deeper burial depth, shows good reservoir quality. Compared with the ZhuJiang Group and the ZhuHai Group sandstone, the EnPing Group sandstone is dominantly coarse sandstone with more quartz grains, minor feldspars and rock fragments. The EnPing Group is dominated by primary pores, which has a better porosity-permeability relationship than other groups. The deep-water of the Baiyun sag still has potential for exploration. In particular, EnPing Group sandstone reservoir may become a desirable goal in deep and ultra-deep exploration.
Dhote, Prashant (Kuwait Oil Company) | Al-Adwani, Talal (Kuwait Oil Company) | Al-Bahar, Mohammad (Kuwait Oil Company) | Al-Otaibi, Ahmad (Kuwait Oil Company) | Chakraborty, Subrata (Schlumberger) | Stojic, Slobodan (Schlumberger)
Subsurface petroleum industry is burdened with uncertainties in every aspect from exploration to production due to limitations of accessibility to reservoir and technology. The most important tools used to understand, quantify and mitigate the uncertainties are geostatistical static modeling and numerical dynamic simulation geomodels. Geomodels are widely used in the industry for characterizing the reservoir and planning favorable development strategy. It is vital instrument for maximizing asset value and optimize project economics.
Static geomodels are foundation for all the advanced numerical and analytical solutions to solve the intricacies of reservoir performance. At the same time, it is where all the static and dynamic geological and engineering observations get integrated to develop common understanding of the reservoir for future studies. Understanding of the above observations and imaging of reservoir framework by individual is the basis for building static geomodels. Hence, at time, the process is highly subjective and proper QC'ing of the models to achieve the general and specific modeling objectives becomes imperative. Simple Questionaries’ based QC'ing and ranking methodologies are also controlled by subjectivity and individual preferences.
In the present endeavor, quantitative ‘Key Performance Indicators (KPIs)’ based standard static geomodeling practices and QC'ing methodologies at corporate level are developed in specially designed "Process Implementation Project (PIP) – Hydrocarbon resource and Uncertainty Management"’ under the aegis of ‘Kuwait Oil Company (KOC) - Reservoir Management Best Practices Steering Committee'.
The main objectives are to establish a practical modeling process, workflows and criteria to standardize modeling processes. A structured self-guidling modeling document has been developed with self-assemment guidelines and questionary. Finally, for each individual process a set of KPIs are specified as minimum standard to meet to obtain the approval of static model.
The present efforts are important for any geologists, geomodelers and reservoir engineers dealing with geostatistical and numerical reservoir modeling and will provide the KPI's based general practices for quality assurance (QA) and QC'ing of the models.
Tuba is tight carbonate reservoir and one of largest Upcoming Reservoirs in North Kuwait Sabriyah field and subdivided to three main reservoir units (upper, middle and lower). Tuba, though discovered in the 60's, is still relatively under-exploited presently with only ±10 active oil producer wells with very low total production rate compared to other major reservoirs in same field. High reservoir heterogeneity, tightness, and poor fluid properties necessitate the application of fracturing stimulation technology to maximize Conductivity and hence recovery enhancement. Recent technologies in multistage acid Fracturing executed successfully covering multiple layers as first time ever in one of existing two Tuba horizontal wells.
The well under study is highly deviated, completed as barefoot in the Upper Tuba reservoir, intersecting multiple sub-layers. Following the positive results of acid fracturing treatments in offset Tuba's vertical wells, the candidate well was selected for first multistage acid fracturing in horizontal wells, to setup the reservoir development plan ensuring high production potential with most cost-effective drilling and completion strategies. Rig-less 5-Stages Acid Fracture treatment was executed in flawless operation. Many technical and operational challenges were faced (Geo-mechanics, stages selection and design, cementing 7in liner) and properly handled within integrated teams with lessons learned are to be considered in next designs and executions. Initial post multistage acid Frack short term production showed productivity improvement by approximately 5 folds of pre-stimulation production. The well showed high decline in production rate within the first one-year production post fracturing stimulation. However, analysis showed that the decline mainly was caused by reservoir depletion rather than fracture conductivity deterioration. The well is under close monitoring for stabilization (rate and pressure). Horizontal PLT is planned to evaluate inflow profile from individual layers to improve next designs.
Despite the close results yilded from the multistage acid fracturing in two horizontal wells compared to the results from 7 vertical wells, it is still early to evaluate stimulation potential of horizontal against vertical wells. It needs more production history and more wells to evaluate long term sustainability.
Water-flooding is planned to support reservoir development and enhancing stimulation sustainability and by turn recovery factory. First pilot water flooding injector well was commissioned in early 2018, but comprehensive waterflooding analysis is not finalized yet.
The initial positive results of first multistage acid fracturing in Tuba reservoir had key contribution to setup Development strategy for the entire TUBA reservoir to expand drilling horizontal wells and complete it with initial multistage fract (MSF) stimulation to maximize reservoir exposure and enhance reservoior productivity that will contribute significantly to the NK production target. Two more horizontal wells were drilled and completed with MSF in late 2018 with initial encouraging enhanced productivity results during cleaning and lifting but were not put yet on production for more comprehensive analysis. ation to improve initial productivity.
Pictures shot in fractured wells show how a high-pressure slurry of water and sand carves up the perforations. The technical challenges imposed by tight well spacing and fracture interactions have become a focal point of recent earnings calls between investors and the leaders of several shale producers. The picture of the future is becoming clearer, and there are fewer oil wells in it. Another reminder that it costs more to coax the same amount of oil from new wells as for older wells nearby, with a closer look at the big plays and how the wells are completed. Noble’s first row of wells in its massive Mustang project is helping increase the operator’s DJ Basin output, and similar results are soon expected in the Delaware Basin.
Well RXY is located in Cairn’s Ravva offshore field in the Krishna-Godavari Basin in India. One goal for the field was significant crude production by means of a secondary reservoir section. This paper compares the results of gas identification and lithology identification using pulsed-neutron spectroscopy in openhole and casedhole environments. Acquiring data from an abandoned subsea well has been done before, but never quite like this. As I read through the abstracts and papers that have been presented in the past year, I notice several key themes: verification of cement placement, development of new materials as a barrier, development of new additives to improve the cement barrier, and enhancement of existing techniques.
Completion engineers feel pressure to maximize production per acre and minimize the downsides of fracturing in tight spaces. Terry Palisch, talks about promoting knowledge sharing as part of JPT’s tech director report. Good diagnostic testing is often painstaking, time-consuming, and costly, but recent studies suggest that a lack of knowledge can be even costlier. Good reservoir detective work costs money, but two studies show how it can help identify even more expensive problems.
Pictures shot in fractured wells show how a high-pressure slurry of water and sand carves up the perforations. This paper presents the evolution of a Bakken advanced completion design with the added enhancement of extreme limited entry (XLE) perforating. With this strategy, an operator has consistently stimulated more than 11 perforation clusters per stage. Good reservoir detective work costs money, but two studies show how it can help identify even more expensive problems. Significant production gains are being made with hydraulicly fractured wells using diversion to stimulate a higher percentage of the perforations.