Using RFT Data for Elastic Rock Properties' Dependency on Pore Pressure in 4D Quantitative Analysis

2006 ◽  
Author(s):  
H. J. Hansen ◽  
L. Gommesen ◽  
Y. El Ouair
Keyword(s):  
Quantitative Analysis ◽  
Pore Pressure ◽  
Rock Properties ◽  
Elastic Rock

Overcoming Hole Instability in Highly Deviated Wells in the Kafr El Sheikh Shale, Offshore Mediterranean, Egypt

2021 ◽  
Author(s):  
Yasser Kholaif ◽  
Mahmoud Elmaghraby ◽  
Annick Nago ◽  
Jean-Michel Embry ◽  
Pramit Basu ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Lower Bound ◽  
Real Time ◽  
Pore Pressure ◽  
Nile Delta ◽  
Stress Sensitivity ◽  
Rock Properties ◽  
Well Drilling ◽  
Geomechanical Monitoring ◽  
Deviated Wells

Abstract Drilling challenges in offshore Nile Delta have been largely documented in the literature. Operators are often confronted with drilling problems related to shale swelling, cavings, tight holes in combination with increased risks of lost circulation in some of the highly depleted formations. The Kafr El Sheikh shale in particular, has been linked to many instances of wellbore instability, due to its mineralogical composition (estimated to be mostly smectite, >70%). From offset well drilling experience, it could also be noticed that insufficient mud weight was often used to drill through the Kafr El Sheikh Shale, causing wellbore failure in shear due to lack of support of the wellbore wall. In the past, multiple mud weight designs have been implemented relying solely on pore pressure as lower bound of the mud window. With the increased use of geomechanics, it has been demonstrated that the lower bound should be taken as the maximum of the pore pressure and borehole collapse pressure, thus accounting for the effects of formation pressure, horizontal and vertical stresses, rock properties as well as wellbore trajectory. It has been proven that slight overpressure is often encountered halfway through the Kafr El Sheikh formation, which would typically result in slightly higher borehole collapse pressures. In the study fields, the operator expressed interest in drilling highly deviated wells (> 60-70 degrees). This raised concerns for increased drilling challenges, especially in the Kafr El Sheikh. A comprehensive and systematic risk assessment, design of a fit-for-purpose solution and its implementation during drilling took place in the fields of interest. Offset well data analytics from the subject fields supported a holistic evaluation of drilling risks associated with the Kafr El Sheikh, providing good understanding of stress sensitivity on deviation, azimuth and lithology. Upon building a robust geomechanical model, calibrated against offset well drilling experience, pre-drill mud weight and drilling practices recommendations were provided to optimize the drilling program. Near real-time geomechanical monitoring was implemented which helped to manage the model uncertainties. The implementation of a holistic risk assessment, including geomechanical recommendations and near real-time geomechanical monitoring, was effective to lead the drilling campaign successfully. As a result, three high angle wells (> 60-70 degrees) were drilled through the challenging Kafr El Sheikh formation without any hole instability. An integrated risk assessment of hole instability, managed in stages (pre-drill and during drilling), has helped to understand and simulate the behaviors of the formation. Proactive decisions have established a controlled drilling environment for successful operations.

Experimental Investigation of Depletion- and Injection-Induced Changes in Poromechanical, Transport, and Strength Properties of High-Porosity Sandstone

SPE Journal ◽  
2021 ◽  
pp. 1-21
Author(s):  
Saeed Rafieepour ◽  
Stefan Z. Miska ◽  
Evren M. Ozbayoglu ◽  
Nicholas E. Takach ◽  
Mengjiao Yu ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Microstructural Analysis ◽  
Optical Microscope ◽  
Strength Properties ◽  
Rock Properties ◽  
Absolute Permeability ◽  
High Porosity ◽  
Confining Stress ◽  
Stress Changes

Summary In this paper, an extensive series of experiments was performed to investigate the evolution of poromechanical (dry, drained, undrained, and unjacketed moduli), transport (permeability), and strength properties during reservoir depletion and injection in a high-porosity sandstone (Castlegate). An overdetermined set of eight poroelastic moduli was measured as a function of confining pressure (Pc) and pore pressure (Pp). The results showed larger effect on pore pressure at low Terzaghi’s effective stress (nonlinear trend) during depletion and injection. Moreover, the rock sample is stiffer during injection than depletion. At the same Pc and Pp, Biot’s coefficient and Skempton’s coefficient are larger in depletion than injection. Under deviatoric loading, absolute permeability decreased by 35% with increasing effective confining stress up to 20.68 MPa. Given these variations in rock properties, modeling of in-situ-stress changes using constant properties could attain erroneous predictions. Moreover, constant deviatoric stress-depletion/injection failure tests showed no changes or infinitesimal variations of strength properties with depletion and injection. It was found that failure of Castlegate sandstone is controlled by simple effective stress, as postulated by Terzaghi. Effective-stress coefficients at failure (effective-stress coefficient for strength) were found to be close to unity (actual numbers, however, were 1.03 for Samples CS-5 and CS-9 and 1.04 for Sample CS-10). Microstructural analysis of Castlegate sandstone using both scanning electron microscope (SEM) and optical microscope revealed that the changes in poroelastic and transport properties as well as the significant hysteresis between depletion and injection are attributed to the existence and distribution of compliant components such as pores, microcracks, and clay minerals.

The Mechanics of Rock Failure Due to Water Jet Impingement

1974 ◽  
Vol 14 (01) ◽  
pp. 10-18 ◽  
Author(s):  
S.E. Forman ◽  
G.A. Secor
Keyword(s):  
Rock Mass ◽  
Stress Field ◽  
Pressure Distribution ◽  
Pore Pressure ◽  
Static Pressure ◽  
Jet Impingement ◽  
Water Jet ◽  
Rock Properties ◽  
Rock Surface ◽  
Pressure Loading

Abstract The initiation of fracture in a rock mass subjected to the impingement of a continuous water jet has been studied. The jet is assumed to place a quasistatic pressure loading on the surface of the rock, which is treated as a saturated, porous-elastic, isotropic, and homogeneous half-space. While this pressure loading is held constant, the impinging water flows through the rock according to Darcy's law and pressurizes the fluid in the pores. The pore pressure distribution couples with the stress field due to the surface loading to produce an effective stress field, which can start tensile fracturing directly under the load. At various time intervals after initial impingement, the effective-stress field is computed using finite element methods and the results, together with the Griffith criterion for tensile failure, produce the loci of the zones of fracture initiation. The behavior of these zones is displayed as a function of the two jet parameters - pressure and nozzle diameter - and the five rock properties: Young's modulus, Poisson's ratio, tensile strength, porosity and permeability, and time. To experimentally verify that pore pressure plays an important role in the mechanism of rock fracture due to jet impingement, thin sheets of copper (0.001 to 0.005 in.) were placed between a continuous jet (up to 20,000 psi) and the surface of a block of Indiana limestone. The purpose of the copper sheet was to allow the pressure of the jet to be transmitted to the rock, but to prevent water from entering the pore structure. Using pressure substantially greater than the threshold pressure of pressure substantially greater than the threshold pressure of limestone (3,500 psi) where penetration always occurred in the absence of the copper sheet, placement of the sheet was sufficient to prevent any visible damage from occurring to the rock surface, provided the jet did not penetrate the copper first. provided the jet did not penetrate the copper first Introduction The method by which a water jet penetrates and fractures a rock mass is highly complicated and poorly understood. This is mainly because the rock is subjected during the impact to several separate processes, each of which can cause failure. Failure can result from the effects of dynamic stress waves, static pressure loading and erosion. The degree of failure caused by each mechanism is, of course, dependent on the rock properties and jet parameters. parameters. In the first few microseconds of impingement, a subsonic jet pressure on the rock surface reaches the so-called "water hammer" pressure on the rock surface reaches the so-called "water hammer" pressure of pvv(c) and then drops to the nozzle stagnation pressure pressure of pvv(c) and then drops to the nozzle stagnation pressure of approximately 1/2 pv2. (p = fluid density, v = jet velocity, and v(c) = velocity of compression waves in the liquid.) During this initial period of impact, large-amplitude compressive waves are caused to emanate from the point of impingement. Upon reflection off a free surface, these waves become tensile and can cause spalling failures. This mode of failure is usually important with pulsed jet impingement. For continuous jets the spalling effects are small and will be neglected for this study. During the impingement process, the water of the jet flows into the accessible pore space of the rock mass. Since in a continuous jetting process the jet applies a quasi-static pressure loading to the rock surface, the water in the pores is pressurized while the surrounding rock mass is simultaneously stressed. The intent of this paper is to describe the role played by this static pressure loading coupled with the pore-pressure distribution, or pressure loading coupled with the pore-pressure distribution, or the "effective stress," in the first moments of penetration. In studying the process, we will take into account the influence of jet parameters and rock properties. In the course of the impingement process, the jet pressure loading is constantly being redistributed over the crater as it is formed. During this progressive removal of material, erosion is also contributing. The process of erosion is in itself highly complex, so no attempt will be made to characterize it here. EFFECTS OF STATIC PRESSURE DISTRIBUTION-ZERO PORE PRESSURE It has been shown by Leach and Walker that a water jet emanating from the nozzle depicted in Fig. 1 applies a quasi-scatic pressure loading to the surface upon which it is impinging. SPEJ P. 10

Cementation exponent as a geometric factor for the elastic properties of granular rocks

Geophysics ◽  
2020 ◽  
Vol 85 (6) ◽  
pp. MR341-MR349
Author(s):  
Tongcheng Han ◽  
Zhoutuo Wei ◽  
Li-Yun Fu
Keyword(s):  
Elastic Properties ◽  
Geophysical Methods ◽  
Effective Medium ◽  
Geometric Factor ◽  
Rock Properties ◽  
Modeling Approaches ◽  
The Earth ◽  
Elastic Rock ◽  
Effective Medium Models ◽  
Electromagnetic Surveys

A geometric factor properly describing the microstructure of a rock is compulsory for effective medium models to accurately predict the elastic and electrical rock properties, which, in turn, are of great importance for interpreting data acquired by seismic and electromagnetic surveys, two of the most important geophysical methods for understanding the earth. Despite the applications of cementation exponent for the successful modeling of electrical rock properties, however, there has been no demonstration of cementation exponent as the geometric factor for the elastic rock properties. We have developed a workflow to model the elastic properties of clean and normal granular rocks through the combination of effective medium modeling approaches using cementation exponent as the geometric factor. Based on the dedicated modeling approaches, we find that cementation exponent can be adequately used as a geometric factor for the elastic properties of granular rocks. Further results highlight the effects of cementation exponent on the elastic and joint elastic-electrical properties of granular rocks. The results illustrate the promise of cementation exponent as a geometric link for the joint elastic-electrical modeling to better characterize the earth through integrated seismic and electromagnetic surveys.

scholarly journals Sensitivity Analysis of Geomechanical Constraints in CO2 Storage to Screen Potential Sites in Deep Saline Aquifers

2021 ◽  
Vol 3 ◽  
Author(s):  
Yashvardhan Verma ◽  
Vikram Vishal ◽  
P. G. Ranjith
Keyword(s):  
Sensitivity Analysis ◽  
Pore Pressure ◽  
Co2 Storage ◽  
Pressure Rise ◽  
Injection Rate ◽  
Early Years ◽  
Rock Properties ◽  
Deep Aquifers ◽  
Plume Migration ◽  
Storage Potential

In order to tackle the exponential rise in global CO2 emissions, the Intergovernmental Panel on Climate Change (IPCC) proposed a carbon budget of 2,900 Gt to limit the rise in global temperature levels to 2°C above the pre-industrial level. Apart from curbing our emissions, carbon sequestration can play a significant role in meeting these ambitious goals. More than 500 Gt of CO2 will need to be stored underground by the end of this century to make a meaningful impact. Global capacity for CO2 storage far exceeds this requirement, the majority of which resides in unexplored deep aquifers. To identify potential storage sites and quantify their storage capacities, prospective aquifers or reservoirs need to be screened based on properties that affect the retention of CO2 in porous rocks. Apart from the total volume of a reservoir, the storage potential is largely constrained by an increase in pore pressure during the early years of injection and by migration of the CO2 plume in the long term. The reservoir properties affect both the pressure buildup and the plume front below the caprock. However, not many studies have quantified these effects. The current analysis computes the effect of rock properties (porosity, permeability, permeability anisotropy, pore compressibility, and formation water salinity) and injection rate on both these parameters by simulating CO2 injection at the bottom of a 2D mesh grid with hydrostatic boundary conditions. The study found that the most significant property in the sensitivity analysis was permeability. Porosity too affected the CO2 plume migration substantially, with higher porosities considerably delaying horizontal and vertical migration. Injection rate impacted both the pressure rise and plume migration consistently. Thus, in screening potential storage sites, we can infer that permeability is the dominant criterion when the pore pressure is closer to the minimum principal stress in the rocks, due to which injection rate needs to be managed with greater caution. Porosity is more significant when the lateral extents of the reservoir limit the storage potential.

scholarly journals Hydraulic and Mechanical Impacts of Pore Space Alterations within a Sandstone Quantified by a Flow Velocity-Dependent Precipitation Approach

Materials ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3100 ◽  
Author(s):  
Maria Wetzel ◽  
Thomas Kempka ◽  
Michael Kühn
Keyword(s):  
Flow Velocity ◽  
Power Law ◽  
Elastic Moduli ◽  
Rock Properties ◽  
Local Flow ◽  
Mineral Growth ◽  
Macro Scale ◽  
Elastic Rock ◽  
The Impact ◽  
Flow Velocities

Geochemical processes change the microstructure of rocks and thereby affect their physical behaviour at the macro scale. A micro-computer tomography (micro-CT) scan of a typical reservoir sandstone is used to numerically examine the impact of three spatial alteration patterns on pore morphology, permeability and elastic moduli by correlating precipitation with the local flow velocity magnitude. The results demonstrate that the location of mineral growth strongly affects the permeability decrease with variations by up to four orders in magnitude. Precipitation in regions of high flow velocities is characterised by a predominant clogging of pore throats and a drastic permeability reduction, which can be roughly described by the power law relation with an exponent of 20. A continuous alteration of the pore structure by uniform mineral growth reduces the permeability comparable to the power law with an exponent of four or the Kozeny–Carman relation. Preferential precipitation in regions of low flow velocities predominantly affects smaller throats and pores with a minor impact on the flow regime, where the permeability decrease is considerably below that calculated by the power law with an exponent of two. Despite their complete distinctive impact on hydraulics, the spatial precipitation patterns only slightly affect the increase in elastic rock properties with differences by up to 6.3% between the investigated scenarios. Hence, an adequate characterisation of the spatial precipitation pattern is crucial to quantify changes in hydraulic rock properties, whereas the present study shows that its impact on elastic rock parameters is limited. The calculated relations between porosity and permeability, as well as elastic moduli can be applied for upscaling micro-scale findings to reservoir-scale models to improve their predictive capabilities, what is of paramount importance for a sustainable utilisation of the geological subsurface.

AN INTEGRATED PETROPHYSICAL WORKFLOW TO GENERATING FLUID SUBSTITUTED LOGS FOR AVO CHARACTERISATION—GIPSY AND NORTH GIPSY FIELDS CASE STUDY, NORTH WEST SHELF, AUSTRALIA

2002 ◽  
Vol 42 (1) ◽  
pp. 477
Author(s):  
D.L Clarke ◽  
A.P Clare
Keyword(s):  
Field Study ◽  
Water Saturation ◽  
Integrated Approach ◽  
Rock Properties ◽  
Intrinsic Permeability ◽  
North West ◽  
Consistent Model ◽  
Original Field ◽  
Elastic Rock

As part of a multi-well field study an integrated petrophysical workflow was developed to include the generation of fluid substituted logs for AVO characterisation.The workflow relied upon the construction of a multimineral model that best approximated the actual mineral content of the reservoir. Any limitations or assumptions were noted and taken into account when creating the multi-mineral model. Other petrophysical results were derived from the same model to validate its consistency such as intrinsic permeability, porosity, water saturation, etc. Iteration between the model and the results was required until a consistent model was achieved.The estimation of an intrinsic permeability log was based upon the k-Lambda method that uses the multimineral model and porosities.The estimation of a shear slowness log and the fluid substituted logs was based upon elastic rock properties derived from the multi-mineral model and the acquired compressional slowness log and bulk density log. This integrated approach provides a higher confidence in the derived results, which are then used as input into the reservoir model, thereby improving the reserve calculations.The interdependence of each derived result on the same input multi-mineral model ensures consistency and predictability in a complex geological environment, which captures all available information.The method is demonstrated with the Gipsy–1 and North Gipsy–1 wells, which were part of the original field study.

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