Oil production from the giant oil fields of Saudi Arabia is said to be one of the big levers that drive the world economy. Saudi Aramco has been providing the support of this lever with over 70 years of oil production. To maintain its level of production, Saudi Aramco has had to place some of its fields on a water injection scheme, for pressure support and to enhance reservoir recovery. Hydrocarbon sweep and water contact movement through these reservoirs is then monitored through saturation logs. In Saudi Aramco, hydrocarbon saturation within the reservoir after water has swept through is typically measured with two types of tools:A Gamma ray (GR) detection tool. This tool acquires GR in two modes, namely the sigma/capture mode and the Carbon-Oxygen/inelastic mode.A resistivity tool. This can be logged in cased hole with a cased hole formation resistivity, and in barefoot completions using the slim induction tools. Both types of monitoring devices, when logged under the right environmental conditions have been found to add significant value to the way we manage our reservoirs. Some of the Saudi Aramco business drivers for logging these tools are:Reservoir management and optimizations.Optimal well placement.Location of the pool of attic or bypassed oil.Calibration of reservoir simulation models.Identification of cost saving workover opportunities. The existing reservoir monitoring tools in the market are dogged with some challenges. The measurement envelope of the GR tools are very shallow, therefore they suffer from washouts and near wellbore fluid effects, while the resistivity tools require a good knowledge of the flood water salinity for accurate saturation computation. Thus, it is critical that these tools are logged under the right conditions. In spite of the above challenges, Saudi Aramco continues to look ahead for cost-effective solutions through collaboration with service companies. This paper will review some of the benefits that Saudi Aramco has derived from over 200 Reservoir Saturation Monitoring (RSM) logs acquired annually, while also highlighting some challenges and opportunities for the future development of these tools.
Traditionally, brown field developments have often required the plug-back and side-track of existing drain-holes, to target any nearby opportunities. With advances in drilling technology, there is a general preference to drill small diameter wells due to the comparative cost advantage of small holes. In the recent times, this preference has led some wireline service companies to start to offer open-hole formation evaluation services with slim tools having diameter in the 2.0 -to- 2.5 in range. At present, most of the traditional petrophysical measurements can be acquired utilizing slim tools. In addition, several "specialized" measurements such as cross dipole sonic, formation pressure testing, and resistivity imaging can also be acquired. The use of battery and memory technologies has allowed these tools to be deployed using a broader range of conveyance techniques allowing for reduced risk in the entry of slim wells. The provision of slim hole logging services has created an opportunity in the industry to leverage these tools for the economic development brown fields. Thus short horizontal sidetracks and well re-entry’s to test deeper horizons can be drilled and logged successfully. Saudi Aramco has been able to leverage these tools in its continued development of the giant Ghawar field. Some of the development projects are listed below; Some horizontal side-tracks with 3–7/8" hole sizes have been drilled under high dog-legs than was previously impossible and logged successfully.It is now possible to run well-completions in newly drilled wells that have well control problem. A provision is made to subsequently log these wells with slim wireline logging tools.It is now possible to run a complete suite of wireline logs across some old wells that were previously completed without a full formation evaluation logging suite.Slim-hole formation resistivity imaging services are now being provided, to aid in the identification of borehole break-out and fractures features that might affect the well’s productivity.Slim hole formation pressure testing have been acquired in slim wells in order to generate a pressure gradient, determine oil mobility, and define oil-water contacts Several case studies would be used in this paper to demonstrate how Saudi Aramco has leveraged these slim wireline tools to realize some development opportunities. Also examples would be used to show that these slim tools do not compromise the quality of log data acquisition.
The growing demand for oil has emboldened producing companies to reenter old wells to further improve productivity and recovery. This requires monitoring the water saturation. Successes in reservoir saturation monitoring petrophysical analysis have increased the confidence to drill sidetracks in watered wells that have bypassed oil potential. Several techniques can be used to perform the analysis.The Pulsed Neutron Capture (PNC) log is one of the most popular slim cased hole formation evaluation logging tools, which allow running the surveys without having to pull out the production string. Under the right conditions, the PNC logs can be run periodically in the time-lapse mode to monitor changes in water saturation and movements in the oil-water contact and gas-oil contact.The wellbore environment may change between runs and this can complicate the analysis. For example, the borehole fluids may be different: gas, oil or brines of varying salinities. Also, changes in the downhole completion hardware can require running the logs through different tubular configurations. One has to be cognizant of all these environmental effects and appropriately correct for them to obtain the true formation properties, and to make comparisons between runs in the timelapse analysis.Different vendors use different correction schemes. In this paper we will discuss case studies with a methodology from one Service Company that uses a weighted database approach, which relies on characterizing the tool response in known environments. The paper shows some of the advantages and disadvantages of this technique, and in particular, when the downhole conditions deviate from the characterized environment. Alternative methodologies will be proposed to get the best possible results, based on this study. Finally, examples from Saudi Arabian wells will be shown where the computed capture cross section and neutron porosity were successfully corrected in challenging borehole conditions.
Traditionally, brown field developments have often required the plug back and sidetrack of existing drain holes, to target any nearby opportunities. With advances in drilling technology, there is a general preference to drill small diameter wells due to the comparative cost advantage. In the recent times, this preference has led some wireline service companies to start to offer open hole formation evaluation services with slim tools having a diameter in the 2" to 2½" range. At present, most of the traditional petrophysical measurements can be acquired utilizing slim tools. In addition, several "specialized" measurements, such as cross dipole sonic, formation pressure testing, and resistivity imaging can also be acquired. The use of battery and memory technologies has allowed these tools to be deployed using a broader range of conveyance techniques allowing for reduced risk in the entry of slim wells. The provision of slim hole logging services has created an opportunity in the industry to leverage these tools for the economic development of brown fields. Therefore, short horizontal sidetracks and well re-entry’s to test deeper horizons can be drilled and logged successfully. Saudi Aramco has been able to leverage these tools in its continued development of the giant Ghawar field. Some of the development projects are listed below: Some horizontal sidetracks with 3⅞" hole sizes have been drilled under higher doglegs than was previously possible, and logged successfully.It is now possible to run well completions in newly drilled wells that have a well control problem. A provision is made to subsequently log these wells with slim wireline logging tools.It is now possible to run a complete suite of wireline logs across some old wells that were previously completed without a full formation evaluation logging suite.Slim hole formation resistivity imaging services are now being provided, to aid in the identification of borehole breakout and fracture features that might affect the well’s productivity.Slim hole formation pressure testing has been acquired in slim wells to generate a pressure gradient, determine oil mobility, and define oil-water contacts. Several case studies will be used in this paper to demonstrate how Saudi Aramco has leveraged these slim wireline tools to realize some development opportunities. Also, examples will be used to show that these slim tools do not compromise the quality of log data acquisition.
Traditionally, brown field developments have often required the plug back and sidetrack of existing drain holes, to target any nearby opportunities. With advances in drilling technology, there is a general preference to drill small diameter wells due to the comparative cost advantage.In the recent times, this preference has led some wireline service companies to start to offer open hole formation evaluation services with slim tools having a diameter in the 2" to 2½" range. At present, most of the traditional petrophysical measurements can be acquired utilizing slim tools. In addition, several "specialized" measurements, such as cross dipole sonic, formation pressure testing, and resistivity imaging can also be acquired. The use of battery and memory technologies has allowed these tools to be deployed using a broader range of conveyance techniques allowing for reduced risk in the entry of slim wells.The provision of slim hole logging services has created an opportunity in the industry to leverage these tools for the economic development of brown fields. Therefore, short horizontal sidetracks and well re-entry's to test deeper horizons can be drilled and logged successfully. Saudi Aramco has been able to leverage these tools in its continued development of the giant Ghawar field. Some of the development projects are listed below:• Some horizontal sidetracks with 3⅞" hole sizes have been drilled under higher doglegs than was previously possible, and logged successfully. • It is now possible to run well completions in newly drilled wells that have a well control problem. A provision is made to subsequently log these wells with slim wireline logging tools. • It is now possible to run a complete suite of wireline logs across some old wells that were previously completed without a full formation evaluation logging suite. • Slim hole formation resistivity imaging services are now being provided, to aid in the identification of borehole breakout and fracture features that might affect the well's productivity. • Slim hole formation pressure testing has been acquired in slim wells to generate a pressure gradient, determine oil mobility, and define oil-water contacts.Several case studies will be used in this paper to demonstrate how Saudi Aramco has leveraged these slim wireline tools to realize some development opportunities. Also, examples will be used to show that these slim tools do not compromise the quality of log data acquisition.
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