Well Design for Shallow Gas

Murray, Steve; Williamson, M.; Gilham, S.; Thorogood, John

doi:10.2118/29343-ms

Cited by 6 publications

(6 citation statements)

References 14 publications

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“…In case (iii) the time between initial kick and full blowout is usually very short and there may be no mechanism to shut-in the well during this time. In instances such as this, the BOP may be closed and flow diverted via a "diverter line" overboard [9,10] . Analyses of these three scenarios will be discussed in this paper.…”

Section: Possible Causes For a Blowoutmentioning

confidence: 99%

“…The final scenario considered in this paper is an analysis of a shallow-gas blowout event. Historically, these events have been fairly common when drilling in US Gulf Coast shelf waters [4][5][6][7]9,10] . Previous publications have investigated the flow rates and pressures generated during these events, with varying degrees of flow-modeling sophistication [13][14][15][16] .…”

Section: Scenario 3 -Shallow Gas Blowoutmentioning

confidence: 99%

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Analysis of Potential Bridging Scenarios During Blowout Events

Willson¹,

Nagoo

Sharma

2013

SPE/IADC Drilling Conference

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This paper demonstrates how simulation of wellbore pressures during different blowout scenarios, borehole stability analysis and solids transport can be applied to the problem of blowout risk assessment. This is a technology area that previously has been overlooked by petroleum geomechanics practitioners. The proposed analysis methodology emphasizes the importance of understanding the transient evolution of the kick within the borehole, as this is a key factor in assessing whether bridging is likely to occur during the events leading up to a blowout. Three representative situations are analyzed and conditions leading to self-killing are reviewed. Analyses of a shallow-gas kick and blowout reproduce the numerous field observations that self-killing is likely from the combination several possible mechanismsborehole collapse of soft shales, sand erosion leading to cavity collapse in the initially-overpressured aquifer zone, gas depressurization and brine influx. For deeper water scenarios a sudden failure of the marine riser while drilling-ahead is expected to result in conditions where self-killing occurs. The rapid reduction in wellbore hydrostatic pressure following the loss of the riser margin is considered sufficient to initiate borehole failure that causes a cavings-loading that chokes the hydrocarbon influx, so allowing settling of the entrained solids and plugging of the borehole. In contrast, a more slowly-evolving swabbed kick is not expected to be self-killing. Here the slow progression of borehole instability is not expected to impede the increasing kick flow-rate. It is hoped that by presenting these analyses the industry may become better informed of the geomechanical and borehole stability aspects of kicks and blowouts, and that as a consequence well designs in deep-water can become more robust and inherently safer.

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Section: Possible Causes For a Blowoutmentioning

confidence: 99%

Section: Scenario 3 -Shallow Gas Blowoutmentioning

confidence: 99%

Analysis of Potential Bridging Scenarios During Blowout Events

Willson¹,

Nagoo

Sharma

2013

SPE/IADC Drilling Conference

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“…Annular gas flow is sometimes encountered before installing the blowout preventer. 2 Gas can migrate in the cemented annulus if the set cement is permeable and has poor bonding with the formation or casing. In other words, the existence/development of microannuli (circumferential fractures), induced fractures, and channels (even with an ultra-low permeable cement matrix) allows the gas to migrate through these features rather than the cement matrix.…”

Section: Introductionmentioning

confidence: 99%

“…Cement sheath plays a key role in maintaining the integrity of a well throughout the well’s life cycle. During the drilling and completion phase of wells, cement integrity becomes more crucial due to the dangerous consequences that might occur when the cement integrity fails. , The ability of cement to seal the annular space plays a critical role in maintaining the well’s integrity by preventing the movement and migration of subsurface fluid and gases to the surface and adjacent formations. Cement sealability can be defined as the ability of cement to seal and prevent fluid propagation through its matrix.…”

Section: Introductionmentioning

confidence: 99%

Numerical Modeling of Gas Migration through Cement Sheath and Microannulus

et al. 2021

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Cement sheath is considered an important barrier throughout the life cycle of the well. The integrity of the cement sheath plays a vital role in maintaining the integrity of wells. Cement’s ability to seal the annular space or a wellbore, also known as cement sealability, is an important characteristic of the cement to maintain the well integrity. It is believed that placing cement in the annular space or wellbore can totally prevent any leakage; however, that is debatable. The reason why cement cannot completely prevent fluid leakage is that cement is considered as a porous medium, and also flaws in cement, such as microannuli, channels, and fractures, can develop within the cement sheath. Furthermore, the complexity of casing/cement and cement/formation interaction makes it very difficult to fully model the fluid migration. Hence, fluid can migrate between formations or to the surface. This article presents a numerical model for gas flow in cement sheath, including the microannulus flow. A parametric study of different variables and their effect on the leakage time is carried out, such as the microannulus gap size, cement matrix permeability, cement column length, and cement porosity. In addition, it presents leakage scenarios for different casing/liner overlap length with the existence of microannulus. The leakage scenarios revealed that the cement matrix permeability, microannulus gap size, and cement length can highly impact the leakage time; however, cement porosity has a minimal effect on the leakage time. In addition, modeling results revealed that the casing/liner overlap length should not be less than 300 ft, and the casing pressure duration should be beyond 30 min to detect any leak.

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“…Shallow flow of water, gas, and fines occurs due to high pore pressure caused by the rapid deposition of undercompacted and overpressurized sands [8]. This shallow flow might be encountered in the early stages of drilling a well; even prior to the installment the blowout preventer [9]. Of all types of well control problems, shallow gas blowouts have been considered as the main cause of the loss of offshore drilling rigs.…”

Section: Introductionmentioning

confidence: 99%

Analytical and Experimental Investigation of the Critical Length in Casing–Liner Overlap

et al. 2019

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Offshore drilling operations exhibit various difficulties attributed to shallow flows worldwide. One of the most common practices for drilling offshore wells is to use liners and liner hangers rather than using full casing strings. This reduces the cost of drilling operation. Liners and liner hangers are required to pass certain standards prior to their deployment in the field. This ensures their ability to withstand harsh downhole conditions and maintain the integrity of the well. A liner hanger contains an integrated seal assembly that acts as a barrier to prevent fluid migration. The cement that is placed within the casing–liner overlap is also considered a barrier, and it is critical that it maintains the integrity of the well by mitigating fluid migration to other formations and to the surface. The failure of this dual barrier (cement and seal assembly) system to seal the annular space can result in serious problems that might jeopardize a well’s integrity. Typically, in field applications, the length of a casing–liner overlap is chosen arbitrarily. In some cases, shorter overlaps (50 to 200 ft) are chosen because of the lower cost and easy identification of leaks during pressure tests. However, some loss of well control incidents (particularly the incident that motivated this study) have been linked to fluid leakages along the casing–liner overlap. This paper investigates the critical length of the casing–liner overlap by modeling gas leakage through the cement placed within the overlap using analytical and experimental approaches. Leakage scenarios were developed to mimic gas migration within the cement in the casing–liner overlap. The results showed that the longer the casing–liner overlap, the higher the leakage time. The results also showed that the current casing pressure test duration of 30 min may not be adequate to verify the integrity of the cement within the overlap. Based on the results and analyses, it is recommended to increase the pressure test duration to 90 min. In addition, the results suggest that the length of the casing–liner overlap should not be less than 300 ft to maintain the integrity of the well in the case of gas influx. Further details are highlighted in the results section. In practice, the current rationale behind the selection of a casing–liner overlap length is not sustainable. Thus, the major advantage of this study is that with field data, it provides both scientific and research-based evidence that can be used to inform the decision behind the selection of the casing–liner overlap length, especially in gas migration-prone zones.

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Well Design for Shallow Gas

Cited by 6 publications

References 14 publications

Analysis of Potential Bridging Scenarios During Blowout Events

Analysis of Potential Bridging Scenarios During Blowout Events

Numerical Modeling of Gas Migration through Cement Sheath and Microannulus

Analytical and Experimental Investigation of the Critical Length in Casing–Liner Overlap

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