Shayegi, Sara (Shell) | Kabir, C. Shah (Hess Corporation) | If, Flemming (Hess Corporation) | Christensen, Soren (Hess Corporation) | Ken, Kosco (Hess Corporation) | Casasus-Bribian, Jaime (Hess Corporation) | Hasan, ABM K. (Hess Corporation) | Moos, Daniel (Dong E&P)
Underbalanced drilling (UBD) offers a unique opportunity to estimate undamaged, in-situ formation properties upon first contact with the formation while drilling. This paper compares well-testing techniques developed for UBD with conventional methods. The reservoir flow rates in combination with flowing bottomhole pressures (BHPs) acquired while drilling can be used to identify productive intervals and estimate dynamic reservoir properties.
Unlike typical UBD projects where reservoir benefits are the primary focus, the driver for this mature field was overcoming the drilling problems associated with the wide reservoir-pressure variability caused by nearby producers and injectors. UBD was piloted as a means to achieving the requisite lateral lengths for reserves capture and meeting production targets. Minimizing formation damage and characterizing the reservoir while drilling were added benefits.
Several reservoir-characterization methods based on rate-transient analysis (RTA) were used to perform well testing while drilling. Rate-integral-productivity-index (RIPI) analysis uses the rate and pressure data acquired during drilling to determine whether additional holes drilled contribute and to ascertain the relative quality of this rock. In the increasing-boundary method, real-time rate and pressure data during drilling, circulating, and tripping allowed assessment of formation properties through history matching. Pressure-buildup data were also available during trips because the concentric annuli allowed the pressure to be monitored below the downhole isolation valve. These data enabled the estimation of reservoir pressure and productivity index (PI) with a proxy vertical-well model for each productive interval drilled. These interpretation methods show close agreement in results and lend credence to the UBD-derived parameters.
Shayegi, Sara (Hess Corp.) | Kabir, C. Shah (Hess Corp.) | If, Flemming (COWI) | Christiansen, Soren (Hess Corporation) | Kosco, Ken (Hess Corporation) | Casasus-Bribian, Jaime (Hess Corporation) | Hasan, Abm Khalid (Blade Energy Partners) | Moos, Hasse (DONG Energy E&P)
Underbalanced drilling (UBD) offers a unique opportunity to estimate undamaged, in-situ formation properties upon first contact with the formation while drilling. This paper compares well-testing techniques developed for UBD with conventional methods. The reservoir flow rates in combination with flowing bottomhole pressures (BHP) acquired while drilling can be used to identify productive intervals and estimate dynamic reservoir properties.
Unlike typical UBD projects where reservoir benefits are the primary focus, the driver for this mature field was overcoming the drilling problems associated with the wide reservoir pressure variability owing to nearby producers and injectors. UBD was piloted as a means to achieving the requisite lateral lengths for reserves capture and meeting production targets. Minimizing formation damage and characterizing the reservoir while drilling were added benefits.
Several reservoir characterization methods based on rate-transient analysis (RTA) were used to perform well testing while drilling. Rate-Integral productivity index (RIPI) analysis uses the rate and pressure data acquired during drilling to determine whether additional holes drilled contributes and ascertain the relative quality of this rock. In the increasing boundary method, real-time rate and pressure data during drilling, circulating, and tripping allowed assessment of formation properties through history matching. Pressure buildup data was also available during trips because the concentric annuli allowed the pressure to be monitored below the downhole isolation valve. This data enabled the estimation of reservoir pressure and productivity index (PI) with a proxy vertical-well model for each productive interval drilled. These interpretation methods show close agreement in results and lend credence to the UBD-derived parameters.
Al-Matar, Bader Suilaman (Kuwait Oil Company) | Al-Atroshi, Kamal (Kuwait Oil Company) | Chetri, Hom B. (Kuwait Oil Company) | El-Aziz, Sabry Abd (Kuwait Oil Company) | Kabir, Mir Md. Rezaul (Kuwait Oil Company) | Shayegi, Sara (Halliburton Co.) | Ibrahim, Emad Bakri (Halliburton Energy Services Group)
Underbalanced drilling technology (UBD) has increased production potential from many oil and gas reservoirs worldwide. Kuwait Oil Company (KOC) decided to pilot this technology in Kuwaiti reservoirs to assess the viability of this technique and its capability to optimize production and development of their reservoirs. To maximize the potential for successful implementation, a scientifically rigorous process was implemented to evaluate the reservoir candidates.
The reservoirs include Upper Burgan, Mauddud, Tayarat, and Radhuma. Since there is a high degree of variation in reservoir quality, hydrocarbon properties, formation pressures and other properties depending on location, candidates from different locations were examined. In the first phase, a high order qualitative ranking of the candidates was performed. The basis of comparison included an examination of the reservoir and fluid properties, production data, review of the core, log and geological/geophysical data, drilling and operational information.
The ranking of the candidates was based on production potential, drilling benefits, potential for instability, early water break through, and other operational, reservoir and drilling considerations. The top-ranked candidates were examined determining the range of potential reservoir behavior during UBD and the corresponding wellbore hydraulics (drilling the well on paper) was performed.
It was concluded that UBD technology was suited for several of the reservoirs but that some of the candidates might not realize as much improvement as others to justify implementation in the first implementation stage. If UBD proves successful on the candidates chosen for the pilot study, the candidates showing a lesser degree of potential will again be considered.
This paper describes the screening methodology used and discusses the results from the candidate evaluation process.
The Margham gas field, discovered in the Emirate of Dubai (U.A.E.) in 1982, was heralded as a major discovery of its time, and to this day, still remains the largest onshore gas field in Dubai. This reservoir is characterized by a relatively low-porosity, over-pressured, highly fractured, and faulted carbonate. Production of the native retrograde gas condensate occurs primarily from three major formations: Shuaiba, Kharaib and Lekhwair in the Thamama limestone.
Commercial production from the field commenced in late 1984 with good performance being attributed to the highly developed and connected fracture network. The original reservoir pressure was in the range of +/- 7300 psi; however, the past decade has seen a marked decline in both pressure and associated production, with today's reservoir pressure averaging in the range of +/- 1800 psi.
With such a marked reduction in reservoir pressure coupled with complex geology, intricate vertical and deviated fracture networks, undefined faulting regimes, and retrograde fluid-phase behavior, the task of optimizing production is particularly difficult. All these factors, coupled with the relatively conventional well geometries, have made this field an ideal candidate for underbalanced directional technology. In early 2006, an underbalanced coiled-tubing campaign was commenced to optimize productivity.
This paper discusses the reservoir results generated by the implementation of underbalanced technology. Past reservoir performance of wells drilled overbalanced will be compared with current results for this field case. Recovery and potential reserve gains will also be discussed. Specific production targets and metrics that were set to evaluate success were completely fulfilled in the first few wells in this multi-well campaign.
The Margham onshore gas field is a limestone reservoir that was first put on production in the early 1980's. Originally, it produced a high condensate yield along with the gas; however, as the reservoir pressure decreased, so did the condensate rates! Eventually, gas was the primary production from this field. Because of the depletion being noted, an infill drilling campaign was commenced to recover by-passed hydrocarbons. It was determined that underbalanced drilling would be the best technique to use to avoid lost circulation problems in these very depleted formations (as low as ~1200 psi at 11,000 ft in some areas), and to minimize formation damage so that the maximum production could be realized. Between 2006 and 2007, an 11-well, coiled-tubing (CTD) underbalanced drilling (UBD) campaign was initiated from a mother wellbore to drill multilaterals. The drilling plan was to be conducted through the production tubing to access the by-passed hydrocarbons.
The Thamama Limestone group is highly fractured with the troublesome overlying Nahr Umr shale cap rock, which has caused drilling problems in the past. The drilling conditions would require careful planning since downhole temperatures reached 289ºF, and there were depleted pressures along with H2S and CO2 in the reservoir. The through-tubing drilling campaign was chosen as the best option, because it would reduce risks and the costs associated with a new well or having to pull existing tubing. The equipment and methods to drill successfully have been described in an earlier paper.1 In the referenced paper, the basic concepts and procedures for proper design of an underbalanced coiled-tubing drilling procedure for a multilateral well are reviewed, and those design concepts were used to formulate the strategies for the project discussed in this paper.
Nine wells were drilled in this underbalanced (UBCTD) campaign using a 3-in. bottomhole assembly (BHA).
In an underbalanced drilling process, the wellbore pressure in the openhole section is kept lower than the reservoir pressure. Unlike conventional overbalanced drilling or managed-pressure drilling (MPD) with reduced overbalance margin, the underbalanced drilling environment provides a unique opportunity to gather data that have the potential to provide important information about the reservoirs encountered during drilling.
When the wellbore is kept in an underbalanced condition, formation fluids are allowed to flow into the wellbore during the drilling process. Proper instrumentation, data acquisition, and drilling procedures allow continuous acquisition of data that can be analyzed for the purpose of extracting reservoir information. This capability to continually access reservoir data is a critical factor for assuring that UBD operations will reap the full benefit to the reservoir influx from the formation while drilling.
Underbalanced drilling (UBD) and managed pressure drilling (MPD) are gaining in popularity as drilling methodologies to overcome some of the problems faced in conventional overbalanced drilling. These techniques are complimentary technologies rather than completely separate techniques, MPD techniques at one time having been classified under UBD. Therefore, with the current terminology and the many similarities they are often confused with one another. Underbalanced drilling is a tool both for reservoir
performance improvement and reservoir characterization as well as for addressing drilling problems. MPD, on the other hand, is primarily a solution for mitigating drilling related problems. Both result in a reduction of non-productive time (NPT). Sometimes a combination of both techniques may be required for the same well.
Different operators have chosen UBD and MPD with the goal of curtailing severe fluid losses and other drilling-related problems associated with conventional overbalanced drilling. Often times, while applying this technique to solve these drilling problems, the reservoir benefits have become apparent and have convinced the operators to go to full underbalance to realize the full reservoir production benefits without any period of overbalance throughout drilling, tripping, and completion operations. They have often found that when using UBD for reservoir production improvement, it is possible to perform comprehensive characterization of the
reservoir while drilling. In some cases, zones that were not seen as productive during overbalanced operations have come to light, and reservoir characterization has enabled appraisal of these formations. Reservoir information obtained during the drilling phase can significantly reduce the time and cost associated with gathering and analyzing "well test?? type data post-completion with conventional methods and these methods have been field tested and results compared to conventional well testing with favorable results.
Underbalanced drilling was initially adopted for resolving drilling problems, but it soon became evident that this technique could also minimize reservoir damage. As originally conceived, underbalanced drilling technology included techniques that were fully underbalanced with influx to the surface as well as methods called "low-head?? and "at-balance?? drilling, in which the bottomhole pressure was kept marginally above or approximately equal to the pore pressure. These techniques later became designated as part of a separate category called managed pressure drilling, which has been adopted by the IADC.
Many would agree that all drilling from conventional to air drilling might be considered as a form of "Managed Pressure Drilling,?? since for a drilling project to be conducted in the safest manner, the pressure must be controlled or managed. However, for purposes of this paper, managed pressure drilling will be considered as a discrete method, referring to applications that are considered as at balance or "low-head?? (marginally overbalanced).
This paper will describe normalized data results from UBD and MPD case histories. It will quantify the differences between the two techniques in terms of equipment requirements, reservoir characterization potential as well as quantifying the technical and economic benefits/limitations of each.
The industry is now becoming more knowledgeable concerning underbalanced drilling (UBD) and managed pressure drilling (MPD). These techniques are gaining popularity because of their capability to control severe fluid losses and other problems that are inherent to conventional overbalanced drilling. As a result, considerable increase in their usage has been noted; however, with these increases, it has become apparent that there is a great deal of confusion concerning the basic concepts of each technique and when each should be used. Generally speaking, UBD can be described as a reservoir performance improvement and characterization tool that also provides drilling benefits. Another advantage is that UBD can offer a unique well testing environment in which the properties of reservoir layers can be determined while drilling. MPD, on the other hand, primarily addresses drilling-related problems that result in nonproductive time (NPT) in drilling scenarios. Sometimes, however, there are well scenarios in which both techniques might be needed in different hole sections.
Reservoir information gained during underbalanced drilling also can help reduce the time and cost associated with gathering and analyzing well-test data post-completion with conventional methods. Techniques have been developed to quantify reservoir properties and characteristics for homogenous and heterogeneous and/or fractured reservoir systems.
This paper focuses on where each concept should be used and what benefits can be expected from their application. Results from UBD and MPD case histories are used to quantify the results from these operations. Differences between the two techniques concerning equipment requirements and reservoir characterization potential are also analyzed.
Drilling wells for oil/gas has been increasingly challenging with the companies moving towards difficult environments. The problems faced in these locations range from very narrow margin between the pore (or collapse) and fracture pressures, pore pressure uncertainty, to high pressure and high temperature wells. Wells drilled in these scenarios using the conventional drilling method often do not get to total depth (TD), and even so, drilling can be extremely risky, with several kick/loss situations.
A new drilling method1 has been developed to overcome these problems, allowing a much safer condition, reducing the risks, and also permitting the wells to be drilled to TD much cheaper. Drilling is taken to the limit in a safe manner, extending each phase as much as possible, using the entire available mud weight window for that well.
The method uses the new concept of micro-flux control, which is based on detecting a minimum loss or influx of fluids, and instantly adjusting the return flow and, consequently, the bottom-hole pressure to regain control of the well. The well is drilled closed at all times, and the return flow from the well is compared to the predicted and ideal one, allowing detecting the discrepancies in a very short time.
This paper describes the basis of this new method and steps taken so far in the development. Field tests will be done very shortly, after the method has been tested in a simulated well condition. The use of this method allows wells to be drilled where today it has been impossible, extending today's technological limits way beyond the current boundary.