Investigation of the Process of Mud Filtrate Invasion from an Open Wellbore into a Fresh Water (original) (raw)

An overview on mud filtration in oil wells and its relations

4th international conference on recent innovations in chemistry & chemical engineering,Iran,Tehran, At Tehran, 2017

Usually in an under-balanced drilling operation, due to pressure difference between mud and formation, amount of drilling mud enters the porous media or high permeable formation and reduces permeability around well bore which is a kind of formation damage. This phenomenon is called drilling mud filtration. In some cases, extreme mud filtration may cause lose circulation which is a dramatic damage. Filtration controlling and keeping it in optimized situation to avoid lose circulation is required to have a successful drilling process. In this research, fundamental concepts of filtration, affecting factors on filtration, methods and relation for measuring filtration and its simulation is discussed.

Formation Damage Analysis Due to Filtrate Invasion in Deviated Wells: A Numerical Approach

During production, drilling, completion, stimulation and work-over operations, the formation is exposed to several types of fluids which have high tendencies to impair and impact gas and oil productivity by reducing pore throat size and relative permeability. Therefore, it is desirable to accurately characterize filtration process during these operations. A mathematical model was developed describing the mechanism of formation damage in deviated wells. Rate of mud cake build up, cumulative filtrate volume and depth of invasion into the formation at different angles of inclination were determined. The model employed numerical approach rather than the conventional analytical method to solve the equations developed using the fully implicit discretization scheme. The effect of filtration on the angle of deviation was determined and this should help in planning and allocation of drilling time in order to reduce formation damage. Also the analysis shows the result of infiltration on cake thickness and filtrate volume at the early, middle and late time of permeation into the formation. The model was validated with the previous analytical model. Results showed that the previous conventional analytical models developed overestimate the formation damage when compared to the numerical model.

Characterization of drilling mud fluid invasion

Journal of Petroleum Science and Engineering, 1987

. Characterization of drilling mud fluid invasion. J. Pet. Sci. Eng., 1: 3-13. A method for the characterization of drilling mud fluid invasion of porous formations was developed. The oil saturation and resistivity profiles are determined as a function of radial distance from the well and time using a finite difference solution of the radial form of the diffusivity equation. The coefficient of dispersion and its variation with respect to time was determined for five sandstones using long cores. The effluent profile of a step increase of injected sodium chloride concentration is analyzed to determine the value of the coefficient. Values reported in the literature for the dependence of the mud filtration rate on time of filtration were used. The method gives a complete analysis of mud filtrate invasion and can be used for improvement of resistivity well log interpretation.

Modeling the Rate of Mud Invasion in a Permeable Formation

World Academics Journal of Engineering Sciences, 2020

The invasion of mud filtrates in to the permeable formation is an inevitable experience during drilling operations. It is usually associated with near-complete formation damage in the immediate vicinity of wellbore and the response of well log tools (especially the low penetration tools) are then greatly influenced by the mud filtrates instead of formation fluids which makes its interpretation more difficult. Hence, it is often necessary to know the possible spatial and time variation of mud filtrate concentrations in the porous media during invasion. This study presents a model technique for the numerical simulation of rate of mud invasion using a pressure transient analogy of mud concentration gradient. The model uses a finite difference element of 1000ft 3 divided into five (5) uniform gridblocks of length, 2ft each. The results of the study showed clearly that from the time and space of invasion process initialisation, the mud concentration diffuses into the porous medium. At early time of invasion, the mud filtrate is continuously diffused into the porous media while at later stage of invasion, mud concentration builds from the inner gridblocks facilitating the formation of filter cake at the wellbore. Further analysis of the results reveals that the displacement of the in-situ formation fluid by the invading mud is not a piston-like phenomenon as shown by the spatial variation of the mud filtrates concentration during the invasion period. However, the concentration gradient can be used to define the extent of mud filtrate invasion into the permeable formation

Deep Bed Filtration Modelling of Formation Damage Due to Particulate Invasion from Drilling Fluids

Transport in Porous Media, 2012

A Deep Bed Filtration model has been developed to quantify the effect of solids invasion from drilling fluids on the permeability of rock formations. The calculated particle trapping profile are compared directly with experimental profiles from scanning electron microscopy and synchrotron X-ray sources. The computed permeability reduction as a consequence of particle invasion is in broad agreement with experiment. Backflow was modelled by reversing the flow rate, starting off with a situation where all particles either remain trapped or are all released. It appears that the experimentally observed 30 % release of particles upon backflow is reproducible within the limits of the two extreme cases. When erosion is included in the model, a peak in the back flow pressure time series can be observed. This peak may be correlated with the experimentally observed Flow Initiation Pressure (FIP), which is the back flow pressure needed to initiate flow after initial inflow filtration. Finally, we conclude that internal reservoir damage, within the limits of our 1-D single phase DBF model, may contribute to the experimentally observed Flow Initiation Pressure (FIP).

A NEW APPROACH TO CALCULATE MUD INVASION IN RESERVOIRS USING WELL LOGS

Muds of different compositions are used in the drilling well process, to support the wall of the borehole along with maintenance of pressure, and to remove rock cuttings generated from the geological formations encountered by the drill bit. The drilling mud invades the formations and modifies the zones surrounding the borehole, mainly, in terms of the physical properties of the rocks, such as porosity and permeability. The identification of this formation damage is important for reservoir characterization, and the subsequent well completion, as well as for the analysis of economic viability. Many years ago, Schlumberger developed a method for determining mud invasion diameter using the Tornado Chart. Today, practitioners in the oil industry use the Tornado Chart to present geophysical logs. Improving upon Schlumberger’s methodology, Crain used mathematical equations to calculate the mud invasion diameter. In this study, we propose a polynomial mathematical method to determine mud invasion diameter. Our method utilizes the same resistivity well logs, namely dual induction log and dual laterology, though different from that of Schlumberger or Crain methods. The approach developed in this study considers the characteristics of the invasion process while quickly and accurately showing results in the form of a log that can be visualized adjacent to other logs measured in the borehole.

SPE 128035 A Theoretical and Experimental Analysis of Dynamic Filtration in Drilling Operations

This paper describes a numerical filtration model validated by data obtained from an experimental dynamic filtration loop. The model predicts the filtercake buildup and filtrate flow rate in the drilling process using non-Newtonian muds. It is also able to calculate filtercake properties like permeability and thickness. The equations, written in cylindrical coordinate, are based on the motion and mass conservation equation of the fluid described by Darcy's law. In addition, the permeability and porosity are correlated to the filtercake pressure. The point at which the mud fluid shear rate and the filtercake shear strength are equal defines the filtercake thickness. In the dynamic filtration loop there is a tube with a permeable wall where the carbonate suspension of different sized particles is filtrated. The suspension is homogenized in a tank mixer and pumped using a positive displacement pump. The filtration model was validated through experimental data. In this paper, we discuss the effects of cross-flow velocity and filtration pressure on the filtrate rate and filtercake buildup. The simulated data of filtrate rate and filtercake thickness agreed well with the experimental data. Introduction One of the drilling fluid's basic functions is to exert hydrostatic pressure over the permeable formations to avoid the formation fluid invasion to the well while the drilling operation takes place. The fluid pressure is normally kept above the formation pore pressure to prevent from kick events (formation fluid invasion to the well), that, in some cases, can lead to an uncontrolled influx (blowout). This concept, called overbalanced drilling, is traditionally employed in most of the drilling operations worldwide and in Brazil. As the bit penetrates the reservoir rock, the drilling fluid invades the formation due to the positive pressure differential between the well and the reservoir rock. Portions of the liquid phase of the drilling fluid are lost to the adjacent formation while part of the solids presented in drilling fluid, constituted by particles smaller than the formation pore size, penetrate the rock during the fluid loss period, rapidly plugging the region around the well. Larger particles accumulate on the wellbore walls, initiating an external cake formation. The invasion of fluid and solid particles during this process causes damage to formation around the well. Two invasion mechanisms are notable in the well. The first, called static filtration, occurs when the fluid pumping is interrupted and, from that point on, filtration occurs due to the difference between the hydrostatic pressure in the well and the reservoir pressure. The filtration rates are controlled by the continuously increasing thickness of the filter cake. The other invasion mechanism, called dynamic filtration, occurs when the fluid is pumped through the well. In this process, the cake thickness is resultant from the dynamic equilibrium between solid particles deposition rate and the erosion rate due to the shear stresses generated by the fluid flow in the wellbore. Thus, the filtration rate to the formation tends to stabilize around a certain value while the cake thickness turns constant. Fig.1 illustrates the process. Table 1 shows several authors that studied dynamic and static filtration phenomenon. Modeling and experimental work are listed.