Digitized Uncertainty Handling of Pore Pressure and Mud-Weight Window Ahead of Bit: North Sea Example

SPE Journal ◽  
2019 ◽  
Vol 25 (02) ◽  
pp. 529-540
Author(s):  
Ane E. Lothe ◽  
Pierre Cerasi ◽  
Manuel Aghito
Keyword(s):  
Pore Pressure ◽  
North Sea ◽  
Failure Criteria ◽  
Horizontal Stress ◽  
Traffic Light ◽  
Data Set ◽  
Pressure Profiles ◽  
Weight Window ◽  
Frictional Coefficients ◽  
Fracture Gradient

Summary A digitized workflow from predrill pore-pressure modeling with a Monte Carlo approach until update of the pressure prognosis while drilling from (for example) sonic or resistivity data is described. The approach has the potential to reduce the uncertainty in the predicted mud-weight window ahead of the bit. For the 3D pressure modeling, a basin modeling software is used, where the pressure compartments in the study area are defined by faults interpreted from seismic. Pressure generation and dissipation are calculated for the study area over millions of years, as the basin was subsiding and compaction was taking place. Key input parameters such as minimum horizontal stress, vertical stress, and frictional coefficients for failure criteria are varied. The output is pore-pressure profiles along the planned well path, with uncertainties. The work presented in this paper was carried out on a North Sea data set. The results show that the uncertainty in the pore pressures will highly influence the uncertainty span in both the fracture gradient and the collapse gradient. Representing the mud-weight window in terms of the most likely collapse and fracturing curve, with corresponding minimum and maximum pore-pressure-derived limits on each side, makes for a more realistic prediction. It presents the uncertainty in the result in a simple visual form, using a “traffic light” approach. While drilling, log data will automatically be used to update the pressure and mud-weight prognosis ahead of bit. The digital updated prognosis can help the drilling crew in decision making during drilling campaigns.

Predrill pore-pressure prediction and pore pressure and fluid loss monitoring during drilling: A case study for a deepwater subsalt Gulf of Mexico well and discussion on fracture gradient, fluid losses, and wellbore breathing

2014 ◽  
Vol 2 (1) ◽  
pp. SB45-SB55 ◽  
Author(s):  
Fernando Enrique Ziegler ◽  
John F. Jones
Keyword(s):  
Gulf Of Mexico ◽  
Pore Pressure ◽  
Horizontal Stress ◽  
Fluid Loss ◽  
Pressure Profiles ◽  
Pore Pressure Prediction ◽  
Fracture Gradient ◽  
Minimum Horizontal Stress ◽  
Fluid Losses

In this case study, the overburden, pore-pressure, and fracture gradients are calculated for several nearby analog wells and subsequently used to generate a predrill pore-pressure prediction for the deepwater subsalt Gulf of Mexico well, Flying Dutchman, located in Green Canyon 511 no. 1 (OCS-G 22971). Two key analog wells penetrated the lower Miocene and have sufficient data to generate pore-pressure profiles. Subsequently, the predrill pore-pressure prediction is found to be in good agreement with the pore pressure estimated from well logs while drilling. During the drilling phase of the Flying Dutchman well, two zones of significant fluid loss and wellbore breathing were encountered and are evaluated as a means of determining the formation types where they are most likely to occur, as well as their related minimum horizontal stress and fracture gradient.

A MODIFIED FRACTURE GRADIENT RELATION AND ITS APPLICATION TO EAST TEXAS AND THE TIMOR SEA

1997 ◽  
Vol 37 (1) ◽  
pp. 536
Author(s):  
R.R. Hillis ◽  
D.G. Crosby ◽  
A.K. Khurana
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Poisson’S Ratio ◽  
Horizontal Stress ◽  
Tectonic Stress ◽  
Poisson's Ratio ◽  
East Texas ◽  
Timor Sea ◽  
Fracture Gradient ◽  
Minimum Horizontal Stress

Theoretical fracture gradient relations are generally based on the assumption that the sedimentary sequence behaves elastically under conditions of lateral constraint. Hence the minimum horizontal stress (σhmin) is given by: where V is Poisson's ratio, σv is overburden stress, pp is pore pressure, and at is far -field tectonic stress. In driling practice, fracture initiation, or leak -off pressures, which are related to σhmin are most commonly predicted by the application of empirical stress /depth relations such as that proposed for offshore Western Australia by Vuckovic (1989): Leak -off pressure (psi) = 0.197D1145, where D is depth in feet. A modified form of the uniaxial elastic relation for the prediction of σhmin is proposed, such that: where the constants c and d are straight line regression constants derived from cross -plotting effective minimum horizontal stress and effective vertical stress. This relation, as opposed to previous empirical approaches to fracture gradient /σhmin determination, yields regression coefficients of physical significance: c represents the average Poisson's ratio term, v /(1 -v), and d represents an estimate of the tectonic (and inelastic) component of the minimum horizontal stress. This application of the modified fracture gradient relation, termed the effective stress cross -plot method, is tested successfully against published data from experimental wells in the East Texas Basin where independent estimates of Poisson's ratio are available. Leak -off pressures have been compiled from 61 wells in the Timor Sea. Leak -off pressures in the Timor Sea are somewhat lower than predicted by Vuckovic's (1989) stress /depth relation for offshore Western Australia, and a new, empirical stress /depth relation, which better fits the Timor Sea data is proposed: The effective stress cross -plot method is also applied to the Timor Sea data, yielding: Detailed pore pressure data were not available for the Timor Sea data -set and the effective stress cross -plot method does not fit the observed data any better than the new empirical stress /depth relation. However, the regression constants suggest an average Poisson's ratio of 0.26 and a relatively insignificant tectonic stress of 1 MPa for the Timor Sea.

Digitized Uncertainty Handling of Pore Pressure and Mud-Weight Window Ahead of Bit; Example North Sea

2018 ◽  
Author(s):  
A. E. Lothe ◽  
P. Cerasi ◽  
K. S. Bjørkevoll ◽  
S. Haavardstein
Keyword(s):  
Pore Pressure ◽  
North Sea ◽  
Uncertainty Handling ◽  
Weight Window

Integrated 3D geomechanical modeling and its application for well planning in Bantumilli South area, Krishna-Godavari Basin, India

2020 ◽  
Vol 39 (3) ◽  
pp. 182-187
Author(s):  
Soumen Deshmukh ◽  
Rajesh Sharma ◽  
Manisha Chaudhary ◽  
Harilal
Keyword(s):  
Pore Pressure ◽  
Elastic Properties ◽  
Horizontal Stress ◽  
Seismic Inversion ◽  
Geomechanical Properties ◽  
Fracture Pressure ◽  
3D Geomechanical Model ◽  
Weight Window ◽  
Minimum Horizontal Stress ◽  
Godavari Basin

Complex geologic structure, a heterogeneous reservoir, and complications related to high pressure during drilling necessitate carrying out geomechanical modeling to understand the physical properties of rocks and fluids present within the Early Cretaceous synrift sequence in the Bantumilli South area of the Krishna-Godavari Basin in India. Reservoirs within the synrift sequence exhibit low permeability and high pore pressure. Identification of safe mud-weight window zones is critical for safe drilling of wells in this part of the basin. A detailed workflow for building a robust 3D geomechanical model and its applications to well planning and hydraulic fracturing are presented. Elastic properties of the reservoirs were estimated by prestack seismic inversion. Elastic properties and pore pressure volumes were used to simulate the 3D stress field. The maximum horizontal stress direction is observed to be 130°N ± 5°, i.e., northwest to southeast, and estimated fracture pressure (minimum horizontal stress) values range between 10,000 and 14,200 psi within the synrift sequence. The study has shown that the Cretaceous section of the reservoir has narrow mud-weight window zones. These zones are governed mainly by a high pore pressure regime in the reservoirs. Additionally, deep-seated basement faults have played an important role in the compartmentalization of the reservoir in terms of geomechanical properties.

scholarly journals 4D Finite element modeling of stress distribution in depleted reservoir of south Iraq oilfield

2021 ◽  
Author(s):  
Raed H. Allawi ◽  
Mohammed S. Al-Jawad
Keyword(s):  
Stress Distribution ◽  
Pore Pressure ◽  
Horizontal Stress ◽  
Oil Field ◽  
Rock Properties ◽  
Target Area ◽  
Compression Tests ◽  
Fracture Pressure ◽  
Weight Window ◽  
Minimum Horizontal Stress

AbstractThe harvest of hydrocarbon from the depleted reservoir is crucial during field development. Therefore, drilling operations in the depleted reservoir faced several problems like partial and total lost circulation. Continuing production without an active water drive or water injection to support reservoir pressure will decrease the pore and fracture pressure. Moreover, this depletion will affect the distribution of stress and change the mud weight window. This study focused on vertical stress, maximum and minimum horizontal stress redistributions in the depleted reservoirs due to decreases in pore pressure and, consequently, the effect on the mud weight window. 1D and 4D robust geomechanical models are built based on all available data in a mature oil field. The 1D model was used to estimate all mechanical rock properties, stress, and pore pressure. The minimum and maximum horizontal stress were determined using the poroelastic horizontal strain model. Furthermore, the mechanical properties were calibrated using drained triaxial and uniaxial compression tests. The pore pressure was tested using modular dynamic tester log MDT. The Mohr–Coulomb model was applied in the 4D model to calculate the stress distribution in the depleted reservoir. According to study wells, the target area has been classified into four main groups in Mishrif reservoir based on depletion: highly, moderately, slightly, and no depleted region. Also, the results showed that the units had been classified into three main categories based on depletion state (from above to low depleted): L1.1, L1.2, and M1. The mean average reduction in minimum horizontal stress magnitude was 322 psi for L1.1, 183.86 psi for L1.2, and 115.56 psi for M1. Thus, the lower limit of fracture pressure dropped to a high value in L1.1, which is considered a weak point. As a result of changing horizontal stress, the mud weight window became narrow.

Realtime Drilling Geomechanics Service, Case Study, Offshore Malaysia

2015 ◽  
Author(s):  
Babak Heidari ◽  
Sook Ting Leong ◽  
Nguyen Truong Son ◽  
M Zafril Aznor
Keyword(s):  
Real Time ◽  
Pore Pressure ◽  
Main Concern ◽  
Drilling Performance ◽  
Weight Window ◽  
Advance Notice ◽  
Complex Structural ◽  
Well Data ◽  
Fracture Gradient ◽  
Real Time Information

Abstract Real Time Drilling Geomechanics (RTDG) provides relevant real time information and integrated workflow to help clients in reducing operational risk and nonproductive time (NPT) through drilling in marginal economical and technically challenging environments. Dulang-B field is a technical challenge due to its complex structural geological environment. All the existing wells failed to penetrate into deep reservoir F40 sands due to wellbore instabilities issues. Overpressure in F-sands remains always the main concern and challenge which led to unsafe drilling environment and significant nonproductive time in the field. Avoiding drilling surprises means more than being prepared for problems when they occur; it means averting them in the first place. Appropriate safe mud weight to drill each formation, must be defined to overcome different overpressure zones and identify the best position for casing seat of each hole section of the well. With the knowledge acquired through pore pressure and fracture gradient modeling, well behavior could be foretold with enough advance notice to allow drilling team to calmly make technically sound operational decisions that lead to optimal drilling performance. This study presents the challenges and the main results of the collaborative drilling approach via RTDG (Real Time Drilling Geomechanics) operation in well DL-B28 ST2. This study focuses on the overpressure and narrow safe mud weight window as well as level of uncertainty over prognosis formation tops which has to be managed by integrating LWD seismicVISION* and RTDG which had clear impacts on decision making process. The real time measurement approach by utilizing actual well data provided the best solution to accurately constrain pre-drill pore pressure and fracture gradient model.

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