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.

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.

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.

Experimental Investigation of Reservoir Stress Path Hysteresis During Production-Injection Periods

2014 ◽  
Author(s):  
Mojtaba P. Shahri ◽  
Stefan Z. Miska
Keyword(s):  
Pore Pressure ◽  
Poisson’S Ratio ◽  
Stress Path ◽  
Horizontal Stress ◽  
Poisson's Ratio ◽  
Injection Process ◽  
Fracture Pressure ◽  
Industry Standards ◽  
Depletion Period ◽  
Stress Changes

There has been an increasing consciousness regarding stress changes associated with reservoir depletion as the industry moves towards more challenging jobs in deep-water or depleted reservoirs. These stress changes play a significant role in the design of wells in this condition. Therefore, accurate prediction of reservoir stress path, i.e., change in horizontal stresses with pore pressure, is of vital importance. In this study, the current stress path formulation is investigated using a Tri-axial Rock Mechanics Testing Facility. The reservoir depletion scenario is simulated through experiments and provides a better perspective on the currently used formulation and how it’s applicable during production and injection periods. The effect of fluid re-injection into reservoirs on the horizontal stress is also analyzed using core samples. According to the results, formation fracture pressure would not be equal to its initial value if pressure builds up using re-injection. The irrecoverable formation fracture pressure has a power law relation with pore pressure drawdown range. In order to avoid higher permanent fracture pressure reduction, it’s recommended to start the injection process as soon as possible during the production life of reservoirs. According to the experimental results, rocks behave differently during production and injection periods. Poisson’s ratio is greater during pressure build-up as compared to the depletion period. According to the current industry standards, Poisson’s ratio is usually obtained using fracturing data; i.e., leak-off test or mini-fracture test, or well logging methods. However, we are not able to use the same Poisson’s ratio for both pressure drawdown and build-up scenarios according to the experimental data. Corresponding to Poisson’s ratio values, the change in horizontal stress with pore pressure during drawdown (production) is higher than during build-up (injection) period. The outcomes of this study can significantly contribute to well planning and design of challenging wells over the life of reservoirs.

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.

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.

scholarly journals Experimental Investigation on Propagation Behavior of Hydraulic Fractures in Coal Seam during Refracturing

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Xun Sun ◽  
Shicheng Zhang ◽  
Xinfang Ma ◽  
Yushi Zou ◽  
Guanyu Lin
Keyword(s):  
Pore Pressure ◽  
Horizontal Stress ◽  
Stress Change ◽  
Hydraulic Fractures ◽  
Coal Seams ◽  
Initiation And Propagation ◽  
Hf Propagation ◽  
Minimum Horizontal Stress ◽  
Maximum Horizontal Stress ◽  
Study Laboratory

Refracturing is an effective technology for reinstituting a percolation path and improving the fracture conductivity in coal measure strata. Hydraulic fracture (HF) propagation is complicated due to the presence of cleats and stress change caused by pore pressure changes. Many scholars have studied HF propagation in the initial fracturing of coal, but the refracturing in coal seams is rarely mentioned. In this study, laboratory refracturing experiments were conducted on large natural coal specimens under various triaxial stress states to investigate the propagation of HFs in coal seams. The mechanical properties of coal were tested before refracturing. The maximum and the minimum horizontal principal stresses are inverted to simulate the stress change caused by the production and pore pressure reduction of the stress condition after initial fracturing. Experimental results showed three different types of HF initiation and propagation during refracturing: (1) under low horizontal stress differences (0-2 MPa), HF propagated along the cleats, and no new HFs were formed on the walls of the initial HFs regardless of changes in the horizontal stress; (2) under high horizontal stress differences (4–8 MPa) with no stress inversion, a major HF was initiated parallel to the orientation of maximum horizontal stress during initial fracturing; new branches propagated along cleats in the orientation of the minimum horizontal stress during refracturing; and (3) under high horizontal stress differences (4–8 MPa) with maximum and minimum horizontal stress inversions, the main HF formed along the orientation of the maximum horizontal stress, and a new HF perpendicular to the initial HF was formed during refracturing. Multiple factors affect fracture morphology during refracturing. Cleats affect the HF growth path and the creation of new branches. The in situ stress determines the initiation and propagation of new HFs.

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