Pore Pressure Prediction Research Articles

The consequences of ignoring rock properties when predicting pore pressure from seismic and sonic velocity

Rock properties are shaped by the geological history of the basin into which they have been deposited. The environment of deposition (and eroded hinterland provinces) controls the mineralogy and resultant rock type, while geological processes such as uplift, denudation, or constant deposition and burial will all shape the development of porosity in rocks. These factors may all play a part, to some degree, in the development of any abnormal pressure (herein termed overpressure; pressure in excess of the hydrostatic pressure) within formations. The more processes that have occurred, the more complicated the task will be to accurately predict this anomalous pressure. Typically, velocity data such as seismic interval velocity and sonic logs are used with industrystandard algorithms in all geological settings and lithology types to predict pore pressure. This paper will set out why standard pore pressure algorithms must only be applied after the rock properties have been assessed fully and examples are given of the circumstances where velocity data, both sonic and seismic, may never allow an accurate pressure assessment. Brief mention will also be made of why additional care must be taken before using seismic velocity to predict pore pressure.

Typical disequilibrium compaction caused overpressure of Paleocene Dongying Formation in northwest Liaodongwan Depression, Bohai Bay Basin, China

Bohai Bay Basin is an important petroliferous basin in China. Petroleum potential in Liaodongwan Depression of offshore Bohai Bay Basin has been proved by previous exploration and production, and overpressures were encountered. Summarized by the DST measurements and mud weight data of over 60 wells in Liaodongwan Depression, the abnormally high pressures preserved in Paleocene Dongying (Ed) Formation distribute over the entire depression and could reach as high as 64.2MPa around the depth of 3420m. Through the well logs analysis, typical corresponding characteristics to disequilibrium compaction can be found: higher in acoustic transit time and lower in density than normal compaction trend. Based on these corresponding features the pore pressure prediction was carried out for all the wells in the area. Sonic velocity-effective stress relationship and sonic velocity-density cross plots were employed to investigate the origin of overpressure in Ed Formation. Sedimentation rates and geothermal features were studied as well. Combining all the analysis, the overpressure of Ed Formation in northwest Liaodongwan Depression was dominantly generated by disequilibrium compaction. With this widely distributed overpressure, thick layers of mudstone of Ed Formation serve as a regional overpressured caprock.

Prediction of pore pressure using well logs and seismic data in Fabi Field, Onshore Niger delta, Nigeria

The variations of pore pressure in Fabi Field Onshore Niger delta have been investigated using well log and seismic data. The both data were calibrated to ensure reasonable match in depth. Zones of overpressure were predicted from the well logs based on the deviations of petrophysical measurement from normal compaction trends. The lateral variations of the overpressure were delineated from seismic data through elastic impedance inversion. Overpressure cube was delineated from the inverted volumes through points of picked horizons. The results of the study revealed overpressure occurrence in well logs at depth level of 8625ft to 9000ft. The elastic impedance inversion presents overpressure variations beyond well control point at the depth level of about 1940-1140ms corresponding to very high impedance value of about 25540-27067ft/s*g/cc. The area extents of the positive anomalies (increase in elastic impedance) are mostly consistent with overpressure zones. Overpressure zones were also estimated from the seismic data between 1560ms -1600ms within the TRK-1 and TRK-2 horizon which also correspond to the well control points (8625ft to nearly 9000ft). The velocity and density crossplots revealed that undercompaction is the main overpressure generating mechanism in Fabi Field, although other parts of the field revealed unloading mechanism.

Estimating density and vertical stress magnitudes using hydrocarbon exploration data in the onshore Northern Niger Delta Basin, Nigeria: Implication for overpressure prediction

Different techniques for predicting density have been driven by the generally poor resolution with depth, and the lack of good quality density data for quantitative formation evaluation studies. The accuracy of most empirical methods is sometimes affected by the methodological uncertainty, but mainly influenced by the reliability of the input data. The benefits of using different methods in density prediction were demonstrated on the basis of a pore pressure prediction study from the Northern Niger Delta Basin (NNDB). The assessment of three density prediction methods (Wyllie, Gardner and Bellotti & Giacca) shows that the Wyllie's method is the preferred choice for the density prediction in the study area because it has the lowest Least Squares Misfit (LSM) error of 0.0019. The vertical stress gradients (constrained from densities) vary vertically with depth from 19 MPa/km (near the surface) to 25.7 MPa/km (at 4 km depth) and laterally between wells, particularly at the top of high magnitude overpressures (at 3.5 km) from 23.6 MPa/km to 25.0 MPa/km. The differences in the vertical stress gradients are consistent with the density variations observed in the area, and they have implications for the predicted pore pressures. We found there to be an increase in pressure gradient from the top to the bottom of wells, which is consistent with data from 87 wells in the area of study. We have therefore been able to identify three main pressure magnitudes in the area of study: (i) low pressure (close to hydrostatic pressure), (ii) abnormal pressure (a little above hydrostatic) and (iii) high pressure (far above hydrostatic).

Origin and distribution of abnormally high pressure in the Mahanadi Basin, east coast of India

Drilling deep wells in the Mahanadi Basin of the east coast of India is highly challenging because of the variations in pore pressure in the Miocene formations. We have observed that the wells drilled in the northern part of the study area have more drilling hazards due to the presence of high pore pressure (modular dynamic test measurements of up to 18.5 ppg) when compared with wells drilled in the southern part of the basin. In the northern part, pore pressure prediction assuming disequilibrium compaction (DC) underpredicts by approximately 2–3.5 ppg when compared with observed pressures; however, in the southern part, pressure prediction matches the observed pressures in the drilled wells. Analysis of sonic velocity-density crossplots suggests that along with DC, some other secondary mechanism also plays an important role in generating excess overpressure in the northern part of the study area; however, the well data do not indicate the presence of an established secondary mechanism, such as fluid expansion, clay conversion, or cementation. The prime difference between the northern and southern areas is the presence of multiple canyon cuts in the northern part and the observation that very high overpressures occur below these canyon cuts. Hence, an attempt was made to ascertain the relationship between the presence of canyon cuts and the observed high pressure with the help of burial history modeling that incorporates the canyon cut features. Pressure estimation based on this approach closely matches the observed pressures in the drilled wells. This very high overpressure observed in the northern part is most likely generated by the combined effect of porosity rebound (due to overburden removal) along with persistence of overpressures that developed prior to erosion. This burial history modeling approach helps in recognizing and understanding the impact of erosional canyon cut events on generation of excess overpressure in the study area. Furthermore, effective stress methods that take secondary pressure generating mechanisms (unloading) into account are used to quantify the difference in pore pressure.

Compaction of smectite-rich mudstone and its influence on pore pressure in the deepwater Joetsu Basin, Sea of Japan

Pore pressure prediction is needed for drilling deepwater wildcats in the Sea of Japan because it is known from past experience that there can be drilling problems can arise due to overpressure at shallow depths. The “Joetsu Basin” area is located offshore to the southwest of Sado Island on the eastern margin of the Sea of Japan. The sedimentary succession of the Neogene is mainly composed of turbidite sediments which contained smectite-rich mudstones. The cause of overpressure in the study area is expected to be a combination of mechanical disequilibrium compaction and chemical compaction, especially from the illitization of smectite.We have constructed basin models and performed numerical simulations by using 1D and 3D PetroMod to understand clearly the history of fluid flow and overpressure development in the lower Pliocene Shiya Formation and Middle to Upper Miocene Teradomari Formations. A compaction model coupled with both mechanical and chemical compaction for smectite-rich sediments is used for pore pressure calibration. We have examined three key relationships: porosity-effective stress, porosity-permeability, and the kinetics of smectite-illite transformation. We determined the ranges for the parameter values in those relationships that allow a good fit between measured and modelled pore pressures to be obtained. Results showed that for the most likely case, high pore pressure in the Lower and Upper Teradomari developed since 8.5 Ma and 5.5 Ma, respectively. Pore pressures in studied structures have approximately doubled since 1 Ma due to the high deposition rate of the Pleistocene Haizume Formation and smectite-illite transformation in the lower Pliocene-Shiya and Middle to Upper Miocene- Lower and Upperr Teradomari formations. In three cases (high case, most likely case and low case), the overpressures in the Shiya, Upper and Lower Teradomari Formations are less than 1 MPa, 15 and 30 Ma, respectively.The results provide a basis for planning future wells in the “Joetsu Basin” area and in other basins where geological conditions are similar, i.e., deepwater, high sedimentation rate, high geothermal gradient and smectite-rich sediments.

De-risking Shallow Hazards through Pore Pressure Prediction and Special Studies — A Case Study from KG-Offshore Basin

Shallow hazards in drilling are caused due to water flow from an over pressured shallow sand encountered at shallow depths below the mudline in deepwater regions of the world. High sedimentation rates and an impermeable mud or clay seal from a condensed section are the main factors contributing to overpressures in shallow water flow sands. If isolated sand bodies are in this shale or mudstone, water from such bodies will not escape easily due to the presence of low-permeability sediments around them. In addition, the high rate of sedimentation from the overburden exerts an enormous pressure on these sediments, causing these isolated bodies containing large amounts of water to be over pressured. The shallow hazards can cause extensive damage to the borehole and pose a great threat to drilling. Their identification/delineation prior to drilling is therefore of utmost importance in reducing risk. The study area has a highly promising Miocene roll structure beneath the shallow hazard zones which warrants probing. Negotiating to this structure through hazardous shallow anomaly already encountered during drilling necessitated for detailed shallow hazard analysis. The area has very limited well data. This limitation in the input data prompted the authors to look for suitable methods to address the issue. An innovative approach to generate pseudo logs from freshly picked seismic velocities was adopted. The pseudo logs were used for carrying out post stack model based inversion. This approach could overcome the limitations of non availability of well data significantly and the generated impedance volume was of optimum quality. The impedance volume could delineate the zones of shallow hazards. The volume was calibrated at the well location indicating low impedance at high pressure zones. This paper describes this innovative/unconventional approach adopted for delineation of these shallow hazards.

Effect of chemical diagenesis on pore pressure in argillaceous sediment

I present a model of pore pressure for argillaceous sediment that integrates the well-known undercompaction mechanism with the lesser-known chemical diagenesis mechanism. The model is based on a generalized compaction model, first-order chemical rate theory and Arrhenius rate equation, and a simple thermal-history model. The parameters of this model (activation energy, E, and the pre-exponential factor, A) are obtained from published X-ray diffraction data. I also present models for bulk density and velocity of sediment that are guided by rock-physics principles. I also discuss the relation between the current model and the Bowers model, which noted the importance of the thermal mechanisms in the context of pore-pressure prediction.

Variability quantification of excess pressure head in heterogeneous deformable aquifers

The direct effect of changes in applied total stresses on fluid-saturated geologic materials is reflected in fluctuations in pore pressure. The quantification of these pressure changes has traditionally been based on the classical poroelasticity theory, developed ignoring the natural variability in aquifer properties (parameters). Uncertainty of excess pore pressure prediction is therefore expected to be large when applying the classical model to field aquifer systems which generally have high degree of heterogeneity. Very limited attention to this issue has been paid. The motivation for this work is to quantify the uncertainty associated with the classical model, the spatial variability of the predicted excess pressure head in the field, where the groundwater flow is produced by the changes in total stress. The stochastic methodology used to develop the results of this study is based on the nonstationary spectral approach. It is found that the heterogeneity and correlation length scale of the log hydraulic conductivity process, and the pore compressibility parameter play essential roles in enhancing the variability in excess pressure head. In addition, the pore pressure head distribution predicted using the classical poroelasticity theory is subject to large uncertainty at a large depth in heterogeneous aquifers.

Full-waveform inversion as a game changer: Are we there yet?

Full-waveform inversion (FWI) has the potential to be a game changer for the seismic industry since it produces accurate velocity models at a resolution that cannot be matched by conventional traveltime tomography, with the additional advantage that it runs on basically raw data. Today, these two features should be better exploited to maximize the business value that FWI can deliver to an oil and gas operator. Provided that we acquire adequate data sets, FWI can be run starting from a smooth velocity model so that traveltime tomography is completely bypassed. As very little processing is required, FWI can be executed in parallel with the main preprocessing efforts, with the results of shortening considerably the overall project turnaround. For imaging purposes, FWI can be limited to the low-frequency range (∼ 10 Hz) but if run in the high-frequency range (∼ 30 Hz), FWI velocities have such a resolution that they can be used directly for interpretation. In particular, applications in the field of pore-pressure prediction and shallow hazard have great potential. In the current implementation, the main limitations are linked to data quality and computational power, but both these issues can be adequately addressed.

Stress and pore pressure histories in complex tectonic settings predicted with coupled geomechanical-fluid flow models

Most of the methods currently used for pore pressure prediction in sedimentary basins assume one-dimensional compaction based on relationships between vertical effective stress and porosity. These methods may be inaccurate in complex tectonic regimes where stress tensors are variable. Modelling approaches for compaction adopted within the geotechnical field account for both the full three-dimensional stress tensor and the stress history. In this paper a coupled geomechanical-fluid flow model is used, along with an advanced version of the Cam-Clay constitutive model, to investigate stress, pore pressure and porosity in a Gulf of Mexico style mini-basin bounded by salt subjected to lateral deformation. The modelled structure consists of two depocentres separated by a salt diapir. 20% of horizontal shortening synchronous to basin sedimentation is imposed. An additional model accounting solely for the overpressure generated due to 1D disequilibrium compaction is also defined. The predicted deformation regime in the two depocentres of the mini-basin is one of tectonic lateral compression, in which the horizontal effective stress is higher than the vertical effective stress. In contrast, sediments above the central salt diapir show lateral extension and tectonic vertical compaction due to the rise of the diapir. Compared to the 1D model, the horizontal shortening in the mini-basin increases the predicted present-day overpressure by 50%, from 20 MPa to 30 MPa. The porosities predicted by the mini-basin models are used to perform 1D, porosity-based pore pressure predictions. The 1D method underestimated overpressure by up to 6 MPa at 3400 m depth (26% of the total overpressure) in the well located at the basin depocentre and up to 3 MPa at 1900 m depth (34% of the total overpressure) in the well located above the salt diapir. The results show how 2D/3D methods are required to accurately predict overpressure in regions in which tectonic stresses are important.

Estimation of upper limit of pore pressure by fault stability analysis

Generally, the pore pressure for a pre-drill well is predicted using empirical parameters, which are regressed from the drilled well's data. However, for areas with large geological differences, empirical parameters which are obtained using traditional methods may fail because intense tectonic movement would result in huge differences between the pre-drill well and drilled well. Firstly, in order to overcome this problem, the method of fault stability analysis is introduced. Analysis indicates that when abnormal overpressure exceeds a certain value, the fault ruptures and the overpressured fluid escapes, so that there is an upper limit of pore pressure (ULPP) for the stable fault. Secondly, the influences of fault angle, formation Poisson ratio and modulus of elasticity on the ULPP are discussed further. The results show that the ULPP of a fault with angle of 65.2° is the minimum, and the critical angle increases with the increase of internal friction coefficient. For reverse faults and strike faults, the influences of Poisson ratio and modulus of elasticity are small, but for normal faults these are significant. Finally, three kinds of ULPP for these different faults are proposed, respectively. The application of this method in the Xihu Sag in the East China Sea has proved that reference to ULPP can verify and correct regressed empirical parameters, so as to improve pore pressure prediction accuracy.

Failure analysis of drillstring in petroleum industry: A review

Abstract Understanding the failure analysis of drillstring and its components i.e., drill collar and drilling bit is one of the essential issues in the oil and gas industry for the high cost of oil well drilling. Different ways such as air drilling, percussion drilling and downhole hydraulic ultra-high pressure (UHP) jet assisted drilling have been often used to improve the rate of penetration (ROP), minimize the cost of drilling per foot and diminish well deviation. Nevertheless, these drilling ways aggravate the working conditions of the downhole drilling tools materials and hence their properties cannot meet the demands of these conditions and consequently causing a risk drillstring failure. The unfavorable geological conditions and the repeated impact for breaking the rock may also cause severe bit bouncing and violent vibration. Tooth loss, tooth fracture, tooth wear and microcracks in addition to drill pipe fatigue from bending stress caused by buckling load are realistic examples of failure modes which occurred in the drilling tools. This study comprehensively describes the reasons causing these failure modes in order to manage risks and achieve high performance of wells and borehole sections. The role of working parameters i.e., bottom hole temperature and solid content on the drilling tools' life time, and the role of predrill predictions of pore pressure or wellbore stability on the drilling process are presented.

Pore pressure prediction of some selected wells from the Southern Pletmos Basin, offshore South Africa

An accurate pore pressure prediction is vital in any risk management plan during the exploration, exploitation and development of wells in the petroleum industry. It is therefore important to understand the factors controlling these pore pressures namely, sediment compaction, overburden, lithology characteristics, hydrocarbon generation, tectonic stress, thermodynamic effects, osmosis and clay mineral transformation, which are all influenced by physical, geological, geochemical and mechanical processes. In this study we present the results of data selected from three wells: Ga-N1, Ga-W1 and Ga-AA1, which were all drilled within the Southern Pletmos sub-basin, offshore South Africa. The pore pressure in the wells was predicted using the Ben Eaton method by creating a depth dependent Normal Compaction Trend (NCT), using resistivity and sonic wireline logs. 2D seismic data were used to develop depth imaging of the pre-drilling pore pressure predictions; this was done using seismic interval velocity data and pressure data to obtain a reflection tomography extraction grid map. Detailed depth plots of overburden gradient (OBG), the Effective Stress (ES), Fracture Gradient (FG), Fracture Pressure (FP), Pore Pressure Gradient (PPG), and the Predicted Pore Pressure (PPP) were thus derived for the three wells. The overburden density varies from 2.09 gm/cc to 2.24 gm/cc between the wells, while the PPP changes from 3,405 psi to 5,062 psi within the selected reservoir intervals. The results show that most of the reservoir intervals of the three wells experience normal pore pressures (between 3000 and 4000 psi), except the reservoir intervals between depths 1868.73 m to 1875.40 m and 1880.3 m to 1887.3 m, respectively, in well Ga-W1, where significant overpressure in the pores exceeding 4000 psi was demonstrated (normal pore pressures are between 3000 and 4000 psi). The tomography extraction grid map that was generated from 2D seismic data of the wells was used to delineate the depth imaging of the pore pressure, in both overpressure and normal pressure formations before drilling, yielded good results.

Image driven subject-specific finite element models of spinal biomechanics

Finite element (FE) modelling is an established technique for investigating spinal biomechanics. Using image data to produce FE models with subject-specific geometry and displacement boundary conditions may help extend their use to the assessment spinal loading in individuals. Lumbar spine magnetic resonance images from nine participants in the supine, standing and sitting postures were obtained and 2D poroelastic FE models of the lumbar spine were created from the supine data. The rigid body translation and rotation of the vertebral bodies as the participant moved to standing or sitting were applied to the model. The resulting pore pressure in the centre of the L4/L5 disc was determined and the sensitivity to the material properties and vertebral body displacements was assessed. Although the limitations of using a 2D model mean the predicted pore pressures are unlikely to be accurate, the results showed that subject-specific variation in geometry and motion during postural change leads to variation in pore pressure. The model was sensitive to the Young׳s modulus of the annulus matrix, the permeability of the nucleus, and the vertical translation of the vertebrae. This study demonstrates the feasibility of using image data to drive subject-specific lumbar spine FE models and indicates where further development is required to provide a method for assessing spinal biomechanics in a wide range of individuals.

Integrated Approach to Pore Pressure and Fracture Pressure Prediction Using Well Logs: Case Study of Onshore Niger-Delta Sedimentary Basin

This study investigated the cause of identified zones of overpressure in some selected wells in a field in the Niger Delta sedimentary basin. Two models were used each for predicting pore pressure and the corresponding fracture pressure using well log and drilling data. Shale lithology in Niger Delta is massive and characterized by high pore pressure; hence shale compaction theory is utilized in this study. The petrophysical data were evaluated using Ikon’s Science Rokdoc software. The two major pore pressure prediction techniques employed are the Eaton’s and Bowers’ models while the Eaton’s fracture pressure model and the Hubbert and Willis fracture pressure prediction models were utilized for fracture prediction. The density and sonic logs were used respectively to generate the shale trend and the shale normal compaction trend used for the prediction. The wells studied showed disequilibrium compaction of sediment to be the major mechanism that gave rise to overpressure in the Niger Delta. Clay diagenesis and fluid expansion were also observed as the secondary overpressure generation mechanism in well X-1. This secondary overpressure mechanism was observed to start approximately at depths of 10,000 ft (TVD). The top of overpressure and the pressure range in the wells studied varied from 6000 to 11,017 ft (TVD) and 1796.70 to 5297.00 psi respectively. The Eaton’s model under-predicts pore pressure at the depth interval where unloading mechanism is witnessed. Since the study revealed presence of secondary overpressure generation mechanism, Bowers model was observed to be the most reliable pore pressure prediction model in the area.

New Pore Pressure Evaluation Techniques for LAGIA-8 Well, Sinai, Egypt as a Case Study

Drilling into a geopressured zone will generally cause a change in a number of basic formation/ drilling relationships. This change is usually seen as a reversal of a gradual depth related trend in a lithologically uniform formation. Of all the geophysical methods, the reflection seismic method is essentially the only technique used to predict pore pressures. The seismic method detects changes of interval velocity with depth from velocity analysis of the seismic data. These changes are in turn related to lithology, pore fluid type, rock fracturing and pressure changes within a stratigraphic column. When the factors affecting the velocity are understood for a given area, a successful pressure prediction can be made. For clastic environments such as the Tertiary section of the Gulf of Mexico or the Niger delta, the interval velocity of the rocks increases with depth because of compaction. In these areas, deviations from normal compaction trends are related to abnormally high pore pressures. The adapted methods provide a much easier way to handle normal compaction trend lines. In addition to well log methods, pressure detection can be obtained via drilling parameters by applying Eaton’s DXC methods. Seismic velocities have long been used to estimate pore pressure, indeed both these quantities are influenced by variations in rock properties such as porosity, density, effective stress and so on, and high pore pressure zones are often associated with low seismic velocities. Pressure prediction from seismic data is based on fundamentals of rock physics and seismic attribute analysis. This paper hence tries to assess the use of seismic waves as a viable means to calculate pore pressure, especially in areas where no prior drilling history can be found. Then we applied these methods on LAGIA-8 well, Sinai, Egypt as a case study. Pore pressure prediction from Seismic is a very essential tool to predict pore pressure before drilling operation. This could prevent the well problem as well blowout and to prevent formation damage, especially in areas where no prior drilling history can be found.

A New 3-D Fluid Potential Calculation Method and Its Application in Petroleum Migration and Accumulation Prediction

With the aim to calculate more accurately 3-D fluid potential and predict the direction of petroleum migration and accumulation, a new method is presented based on Hubbert’s fluid potential model and a comprehensive 3-D pore pressure prediction method. An improved global pore pressure prediction algorithm is used in conjunction with an integrated 3-D pore pressure prediction method to reduce 3-D pore pressure uncertainties and improve 3-D fluid potential accuracy. Then, 3-D fluid potential is obtained according to the relationship between 3-D fluid potential and 3-D pore pressure through programming. The new 3-D fluid potential calculation method has high continuity and accuracy both vertically and horizontally which is helpful in analyzing the characteristic of formation fluid potential and predicting the oil and gas migration and accumulation. The application of the new method in Boxing Sag presents satisfactory result for prediction of petroleum migration direction and favorable oil accumulation.

Oil-based critical mud weight window analyses in HTHP fractured tight formation

Abstract There are plenty of tight oil and gas reserves in western China. The depths of the target reservoirs are usually as deep as 6000–7000 m, which are featured by: HTHP drilling environments, low matrix permeability, well-developed natural fracture systems, and anisotropic in-situ stresses. Even using highly inhibitive oil-based fluids during drilling operation, mud losses and wellbore collapses still occurred frequently. Moreover, in many wells when the mud weight is added, borehole conditions become worse. Contrary to the traditional field experiences, collapse pressure itself has a window. The purpose of this work is to investigate the features of fractured tight formation and correspondingly build a model to explain the unusual drilling complexities. In this approach, the formation is divided into a tight member and a fractured member. 1. In the tight member, a model for pore pressure and stress distribution prediction around a borehole is used based on the poroelasticity theory. The calculation results show that in the near borehole region, instantaneously after the borehole is opened, an abnormal high pore pressure is induced due to the poro-mechanical coupling effect under anisotropic in-situ stress field. The induced pressure is harmful to borehole stability, and a mud weight lower bound is necessary to overcome it. 2. In fractured member, a 3D weak plane model is established considering natural fracture׳s (weak plane) orientation and mud invasion. The calculation results show that muds with hight weight will infiltrate into the aperture of fractures and decrease the normal stress on it, which may induce shear slip failure along the weak plane. Thus an upper bound of mud weight is derived. 3. The time dependent temperature drop at the bottom of a wellbore is also simulated and its impact on borehole stability of tight and fractured section is studied respectively, which helps constrain the mud weight auxilarily. By integrating the above-mentioned factors, a comprehensive critical mud weight window is obtained, which can serve as the theoretical basis for wellbore stability analyses in the fractured tight formation drilled with oil-based fluid.

SEAM Update

In the July issue of The Leading Edge, we discussed the approach we are taking for the development of the geophysical model for the SEAM Pore Pressure Prediction project. We will use the SEAM Phase I model and modify it to include realistic pore-pressure scenarios. To do this, we will use basin simulation to obtain estimates of pore pressures within the model that are caused by various mechanisms that generate pore pressure. To better understand how various input parameters to basin simulation impact the resulting pore pressure as a function of location of position predicted by the model and ultimately the geophysical model, SEAM will issue a request for bids for 2D basin simulation, followed by application of appropriate rock physics to develop both pore pressure and seismic models. By initially conducting 2D simulations, we hope we can investigate how several parameters influence the resulting models. For example, how does the inclusion of clay transition impact the resulting models? Other parameter ranges that we wish to explore include the relation between stress and porosity and the relation between porosity and permeability. We also wish to explore how subdividing the rock types into various groupings influences the final pore-pressure model.