Abnormal pore pressure and fracture pressure prediction for Miocene reservoir rock, field X in Vietnam

During drilling, there must be an evaluation of the maximum pressure that the formation can handle during a well kill scenario. This will depend on various parameters like fracture pressure, pore pressure, kick volume and several other factors. The depth of the next planned hole section will depend on if a kick of a certain size can be handled safely. This evaluation is often referred to as performing kick tolerances. When starting to drill a section, one will take a leak off test to get an indication of the fracture pressure at the last set casing shoe and this will be important information for the kick tolerance results. For HPHT wells the margin between pore and fracture pressures will be small, and one often has to resort to using transient flow models to perform the kick tolerances. However, there are many uncertain parameters that are affecting the results. Some examples here are pore pressure, type of kick and kick distribution. There is a need for trying to incorporate the uncertainty in the calculation process to give a better overview of possible outcomes. This approach has become more and more popular, and one example here is reliability based casing design. This paper will first describe the kick tolerance concept and its role in well design planning and operational follow up. An overview of all parameters that can affect the results will be given. In water based mud, the gas kick will be in free form yielding higher maximum casing shoe pressures compared to the situation when oil based mud is used where the kick can be fully dissolved. Then it will be shown how both an analytical and a transient flow model can be used in combination with the use of Monte Carlo simulations to generate a probabilistic kick tolerance calculation showing possible outcomes for maximum casing shoe pressure for different kick volumes. Here uncertain input parameters that can affect the calculation result will be drawn from statistical distributions and propagated through the flow model to estimate the casing shoe pressure. Multiple runs will be needed in the Monte Carlo simulation process to generate a distribution of the maximum casing shoe pressure. This will demand a rapid and robust flow model. The resulting maximum casing shoe pressure distribution will then be compared against the uncertainty in the fracture pressure at the last set casing shoe to yield a probability for inducing losses. The numerical approach for predicting well pressures and a schematic of the total calculation process will be given. Emphasis will also be put on discussing how this should be presented to the engineer with respect to visualization and communication. It will also be shown that one of the strengths of the probabilistic approach is that it is very useful for performing sensitivity analysis such that the most dominating factors affecting the calculation results can be identified. In that way, it can help in interpreting and improving the reliability of the kick tolerance simulation results.

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Critically stressed fractures: analysis of the Shaikan Field, Kurdistan Region of Iraq

Journal of the Geological Society ◽

10.1144/jgs2019-136 ◽

2020 ◽

Vol 177 (6) ◽

pp. 1315-1328

Author(s):

Callum J. D. Gilchrist ◽

John W. Cosgrove ◽

Kevin J. Parmassar

Keyword(s):

Pore Pressure ◽

Fractured Reservoirs ◽

Significant Proportion ◽

Fracture Network ◽

Maximum Principal Stress ◽

Oil Field ◽

Reservoir Rock ◽

Kurdistan Region ◽

Previous Theory ◽

Content Type

The Shaikan Field is a large producing oil field in the Kurdistan region of Iraq. It consists of multiple fractured reservoirs consisting of limestones, calcareous sandstones and mudstones. The surrounding tectonic terrane is situated in the seismically active Zagros–Taurus orogenic zone, where present-day stresses are high. The regional stresses are found to impose conditions that satisfy failure along reservoir-bound fractures, suggesting that a significant proportion of fractures are likely to be critically stressed. The in situ maximum principal stress magnitudes are estimated using three methods, namely, the tensile and compressive strengths of reservoir rock, and leak-off test (LOT) data. Stress-field orientations are determined from wellbore image log data, which are used to interpret wellbore breakouts and the associated induced tensile fractures. Reservoir pressure has declined since production started and poroelastic responses have been assessed and used to estimate the present-day stress-state and the criticality of those fractures that are most likely to fail or slip. Although a conventional approach has been used the present authors argue that a new approach to stress response with changing pore pressure should be taken. Unlike the previous theory of criticality in which a reduction in pore pressure is considered to lead to a stabilization of the fracture network, the present study suggests that a system may remain critically stressed regardless of pressure decline.Thematic collection: This article is part of the The Geology of Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/the-geology-of-fractured-reservoirs

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Pre-drill pore pressure prediction and safe well design on the top of Tulamura anticline, Tripura, India: a comparative study

Journal of Petroleum Exploration and Production Technology ◽

10.1007/s13202-019-00816-0 ◽

2019 ◽

Vol 10 (3) ◽

pp. 1021-1049

Author(s):

Mohatsim Mahetaji ◽

Jwngsar Brahma ◽

Anirbid Sircar

Keyword(s):

Pore Pressure ◽

Seismic Data ◽

New Method ◽

Burst Pressure ◽

Velocity Data ◽

Pressure Data ◽

Collapse Pressure ◽

Fracture Pressure ◽

Well Design ◽

Pore Pressure Prediction

AbstractThe Tulamura anticline falls in the state Tripura, Northeast India. The anticline is extended up to neighbour country Bangladesh. The region is characterized by huge anticlines, normal faults and abnormally pressured formations which causes a wide margin of uncertainties in wildcat well planning and design. These geological complexities of Tulamura anticline make the drilling engineers more challenging. Therefore, a proper well design is essential in such a region to prevent blowout. Drilling engineer requires to maintain wellbore pressure between the pore pressure and fracture pressure to reduce the possibility of a kick and a formation damage. Pore pressure plays an important role to design a safe and economical well in such a high pressure and temperature reservoir. For wildcat drilling, only seismic data are available in the study area. There are various methods to predict pore pressure from seismic velocity data. Modified Eaton’s method is widely used for the pore pressure prediction from seismic data in terms of the velocity ratio. Modified Eaton’s equations may cause an error by manual selection of compaction trend line which is used to find normal compaction velocity. The main objectives of this study are to develop a new method to predict pore pressure and safe well design on the top of Tulamura anticline in terms of pore pressure. The new method is validated by a well-known method, modified Eaton’s method, and RFT pressure data from offset wells. An excellent match with pore pressures estimated from RFT pressure data and predicted by new model along with modified Eaton’s method is observed in this research work. The efficiency and accuracy level of the hybrid model is more as compared to other methods as it does not require compaction velocity data; thus, an error caused by manual compaction trend can be eliminated. Pore pressure predicted by new method indicates result up to the 6000 m, which is up to the basement rock. The predicted pore pressures by new method are used as an input to calculate the fracture pressure by Hubbert and Willis method, Mathews and Killy method and modified Eaton’s method. Equivalent mud weight selection is carried out using median line principle with additional 0.3 ppg, 0.3 ppg and 0.2 ppg of swab pressure, surge pressure and safety factor, respectively, for calculation of all casing pipes. Casing setting depths are selected based on pore pressure gradient, fracture pressure gradient and mud weight using graphical method. Here, four types of casing setting depths are selected: conductor, surface, intermediate and production casings at 100 ft, 6050 ft, 15500 ft and 18,500 ft, respectively, by new methods, but the casing setting depths for intermediate are at 13500 ft in the case of modified Eaton’s method. The casing policy is selected based on burst pressure, collapse pressure and tension load. For each casing, kick tolerance in bbl is determined from kick tolerance graph to prevent the blowout. Finally, comparative safe and economical wells are designed on the top of Tulamura anticline along with target depth selection, casing setting depth selection, casing policy selection and kick tolerance in consideration of collapse pressure, burst pressure and tension load which gives a clear picture of well planning on the top of anticline in pore pressure point of view.

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Unlocking hydrocarbon reserves by Optimizing Pore pressure and Fracture Pressure Predictions in Mature Mahakam Delta Fields

Proc. Indon. Petrol. Assoc., Digital Technical Conference, 2020 ◽

10.29118/ipa20-g-190 ◽

2020 ◽

Author(s):

W. Pramono

Keyword(s):

Pore Pressure ◽

Oil And Gas ◽

Distribution Analysis ◽

Well Control ◽

Fracture Pressure ◽

Offshore Production ◽

Cumulative Production ◽

Mahakam Delta ◽

Productive Time ◽

Hydrocarbon Reserves

The Mahakam PSC is a mature oil and gas concession in the Mahakam Delta which has been producing for more than 40 years. More than 100 wells per year are drilled from deltaic to offshore production fields (Tunu, Tambora, Handil, Peciko, Bekapai, Sisi-Nubi, and South Mahakam). A total cumulative production of 19 TCF of gas and approximately 1.5 Billion barrels of oil have been produced since 1974. The Peak of Mahakam PSC production started from 2005 and the PSC has been facing natural decline from 2010 to the current date. Several strategies have been implemented to maintain the production rate, and one of them is unlocking less developed reservoirs in the deeper target. Overpressure is one of the challenges to reach the deeper target reservoir. Drilling in an overpressure zone often has serious and unpredictable outcomes. In addition, it has also been exacerbated by massive production in the main zone reservoirs for many years. This massive production has reduced reservoir pressure that led to the decreasing of fracture pressure. These two subsurface challenges effect the narrow window for drilling in the Mahakam operational area and it will certainly also affect the safety, cost and economics of the wells. So, optimizing pore pressure and fracture pressure predictions become the key to unlock less developed reservoirs in mature Mahakam fields. Pore Pressure and Fracture Pressure predictions are developed by understanding the geopressure concept, predicting pore pressure, estimating fracture pressure, developing 3D pore pressure model and performing reservoir distribution analysis. During 2019, eight challenging wells had been drilled and succeeded in unlocking 7.7 BCF of gas reserves. Besides that, Non Productive Time (NPT) of the well control is also decreased yearly and affects the well’s cost efficiency. The improvement of the methodology has been implemented comprehensively to support upcoming challenging exploration and is also expected to sustain the future development of mature Mahakam Fields.

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Drilling the Un Drillable: A Case Study of the Bela Well in Makran Accretionary Prism

10.2118/202084-ms ◽

2021 ◽

Author(s):

Umair Ahmed Baig ◽

Ghulam Nabi Agha

Keyword(s):

Pore Pressure ◽

Accretionary Prism ◽

Well Being ◽

Lessons Learned ◽

Planning Stage ◽

Lost Circulation ◽

Hole Pressure ◽

Bottom Hole Pressure ◽

Fracture Pressure ◽

Bottom Hole

Abstract The Bela Well is situated on Makran accretionary prism with several active mud volcanoes that makes conventional drilling challenging due to the extremely high pore pressure i.e. in excess of 15,000 psi and a very narrow window between pore pressure and fracture pressure. This adverse condition was observed in the 9 offset wells drilled within this basin with problems related to wellbore instability, lost-circulation zones and over-pressured formations leading to kick/loss well control scenarios that resulted in the well being abandoned prior to reaching the geological target. The constraint to drill the planned and 8-3/8" section in the well was the unpredictability of the pore/fracture pressure in the Panjgur formation representing a high-level operational risk. Solutions to tackle such a high pressure well included incorporating heavy grade casing i.e. 9-7/8"- 72 ppf in the planning stage, utilization of a 3000 HP rig to cater to extreme axial and hydraulic loads. Whereas MPD was planned as a technique to cater to the narrow window between pore pressure and fracture pressure. A managed pressure drilling (MPD) system was utilized to enable drilling the 8-3/8" hole section. An MPD system that applies constant bottom hole pressure enabled drilling the section with statically underbalanced mud weight by keeping a constant surface back pressure to prevent any influx. The drilling window for MPD was validated by determining the Bottom Hole Pressure where both, an influx from the formation and fluid losses occurred. These values were later used to establish the target Equivalent Circulating Density-ECD to drill the hole accordingly. Trips for BHA change or BOP test were performed by placing a pressurized mud cap in the wellbore. This paper describes in detail the successful MPD application resulted in the first well being drilled in the Makran accretionary prism to a depth of 5000 m. Lessons learned and challenges encountered will also be discussed in this paper

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Reclaiming the Operating Window: A Managed Pressure Cementing Workflow to Achieve Zonal Isolation Success in a Mature Field

10.2118/206396-ms ◽

2021 ◽

Author(s):

Jeffrey Smith ◽

Lucas Rossi ◽

Christopher Mehler ◽

Jon Todd Eberhardt ◽

Christopher Scarborough ◽

...

Keyword(s):

Best Practices ◽

Pore Pressure ◽

Stability Control ◽

Wellbore Stability ◽

Optimized Design ◽

Additional Time ◽

Fracture Pressure ◽

Increased Risk ◽

Zonal Isolation ◽

Operating Window

Abstract Successfully cementing production casing strings is one of the main challenges of well construction in mature fields. The implementation of cementing best practices can be difficult in the narrow pore pressure-fracture pressure (PPFG) window associated with reservoir depletion and complex well architecture. The increased risk of losses can lead operating teams to compromise on these best practices, often jeopardizing the zonal isolation objectives. This can result in significant additional time, cost, and production deferral/loss. Managed pressure cementing (MPC) is a viable technique to address these challenges. Using the managed pressure drilling (MPD) system's capability to precisely control bottomhole pressure, coupled with the use of mud weights that are lower than conventionally needed can expand the PPFG window; enabling operating teams to achieve a higher success rate in meeting the zonal isolation objectives. This paper will offer an optimized design methodology and critical considerations and parameters for MPC operations. It will also briefly describe the primary applications of MPC and specific, unique design considerations associated with each, namely, (1) mud weight less than pore pressure (PP), (2) losses prevention, and (3) wellbore stability control. Lastly, it will provide a case history illustrating how MPC was used in one of the operator's mature fields, by giving an overview of the job engineering design process, the operational planning (inclusive of contingencies), and the key highlights and learnings observed during execution.

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Pore-pressure-constrained, rock-physics-guided velocity model building method: Alternate solution to mitigate subsalt geohazard

Interpretation ◽

10.1190/int-2014-0078.1 ◽

2015 ◽

Vol 3 (1) ◽

pp. SE1-SE11 ◽

Cited By ~ 10

Author(s):

Nader Dutta ◽

Bhaskar Deo ◽

Yangjun (Kevin) Liu ◽

Krishna Ramani ◽

Jerry Kapoor ◽

...

Keyword(s):

Pore Pressure ◽

Model Building ◽

Rock Physics ◽

Velocity Model ◽

Image Point ◽

Earth Model ◽

Velocity Modeling ◽

Integrated Method ◽

Fracture Pressure ◽

Physics Model

We developed an integrated method that can better constrain subsalt tomography using geology, thermal history modeling, and rock-physics principles. This method, called rock-physics-guided velocity modeling for migration uses predicted pore pressure as a guide to improve the quality of the earth model. We first generated a rock-physics model that provided a range of plausible pore pressure that lies between hydrostatic (lowest possible pressure) and fracture pressure (highest possible pressure). The range of plausible pore pressures was then converted into a range of plausible depth varying velocities as a function of pore pressure that is consistent with geology and rock physics. Such a range of plausible velocities is called the rock-physics template. Such a template (constrained by geology) was then used to flatten the seismic gathers. We call this the pore-pressure scan technique. The outcome of the pore-pressure scan process was an “upper” and “lower” bound of pore pressure for a given earth model. Such velocity bounds were then used as constraints on the subsequent tomography, and further iterations were carried out. The integrated method not only flattened the common image point gathers but also limited the velocity field to its physically and geologically plausible range without well control; for example, in the study area it produced a better image and pore-pressure prognosis below salt. We determined that geologic control is essential, and we used it for stratigraphy, structure, and unconformity, etc. The method had several subsalt applications in the Gulf of Mexico and proved that subsalt pore pressure can be reliably predicted.

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