J.M. Peden

Measurement and correlation of gas condensate relative permeability by the steady-state method

High pressure core flood experiments using gas condensate fluids in long sandstone cores have been conducted. Steady-state relative permeability points were measured over a wide range of condensate to gas ratios (CGR), with the velocity and interfacial tension (IFT) being varied between tests in order to observe the effect on relative permeability. The experimental procedures ensured that the fluid distribution in the cores was representative of gas condensate reservoirs. Hysteresis between drainage and imbibition during the steady-state measurements was also investigated, as was the repeatability of the data. A relative permeability rate effect for both gas and condensate phases was observed, with the relative permeability of both phases increasing with an increase in flow rate. The relative permeability rate effect was still evident as the IFT increased by an order of magnitude, with the relative permeability of the gas phase reducing more than the condensate phase. The influence of end effects was shown to be negligible at the IFT conditions used in the tests, with the Reynolds number indicating that flow was well within the so called laminar regime at all test conditions. The observed rate effect was contrary to that of the conventional non-Darcy flow where the effective permeability should decrease with increasing flow rate. A generalised correlation between relative permeability, velocity and IFT has been proposed, which should be more appropriate for condensing fluids than the conventional correlation. The results highlight the need for appropriate experimental methods and relative permeability relations where the distribution of the phases are representative of those in gas condensate reservoirs. This study will be particularly applicable to the vicinity of producing wells, where the rate effect on gas relative permeability can significantly affect well productivity. The findings provide previously unreported data on relative permeability and recovery of gas condensate fluids at realistic conditions.

The effect of velocity and interfacial tension on relative permeability of gas condensate fluids in the wellbore region

Abstract High-pressure core flood experiments using gas condensate fluids in long sandstone cores were conducted to determine the effect of flow rate and interfacial tension on relative permeability. The data are applicable to near wellbore flow in gas condensate reservoirs, because viscous forces increased over capillary forces during the tests. A relative permeability rate effect for both gas and condensate phases was observed when using steady-state and unsteady-state testing methods. The tests were repeated at increasing flow rates which showed that the relative permeability of both phases increased with the increase in flow rate. Increasing the value of interfacial tension between the phases reduced the relative permeability of the gas phase more than the condensate phase; but the relative permeability of both phases continued to increase at higher flow rates. The influence of core end-effects was shown to be negligible at the low IFT conditions used in the tests. The Reynolds number indicated that flow was within the laminar regime at all test conditions. The observed rate effect was contrary to that of the conventional non-Darcy flow where the effective permeability decreases with increasing flow rates. Relative permeability tests conducted with conventional gas oil fluids at similar test conditions did not exhibit any significant rate effects. This study is applicable to the vicinity of producing wells, where the rate effect on gas relative permeability can significantly affect well productivity.

The Analysis of the Invaded Zone Characteristics and Their Influence on Wireline Log and Well-Test Interpretation

This study examines the invasion of a hydrocarbon bearing formation by drilling fluid filtrate, and investigates, with the aid of a numerical model, the significance of capillary forces on the resulting displacement. It is observed that in high permeability zones, capillary imbibition can draw filtrate into the formation faster than it is lost through the filtercake, which is assumed to control the fluid loss rate. On the basis of conclusions drawn from the numerical study, the phenomena of supercharging (the difference between the water phase pressure at the sandface and the undisturbed formation pressure) has been reanalysed, and an equation recognising supercharging as a two phase problem is presented. Depending on the character of the displacement, supercharging in a hydrocarbon zone can be enhanced or reduced due to the presence of mud filtrate. A field example is used to v

Settling Velocity of Variously Shaped Particles in Drilling and Fracturing Fluids

The settling velocities of a variety of shaped particles to simulate drilled cuttings are measured in both Newtonian and non-Newtonian fluids. The results showed that the particle drag coefficient is a function of the particle Reynods number and, in the case of power-law-model fluids, of the flow behavior index. A new generalized model has been developed for predicting the settling velocities of particles of various shapes in both Newtonian and power-law fluids over a range of flow regimes.

An experimental investigation of waterflooding of gas condensate reservoirs and their subsequent blowdown

Abstract The phase and flow behaviour of water, gas and condensate in pores at reservoir conditions have been visually investigated using glass micromodels, with the pore dimensions and pore geometry of the micromodels being varied between tests. The displacement of hydrocarbons, both above and below the dewpoint, by the advancing water was studied. The model at residual hydrocarbon saturation was depleted and the remobilisation behaviour of the trapped gas-condensate phases was investigated. Preliminary core-flooding results obtained at conditions similar to the micromodel tests confirm the observed phenomena. The micromodel investigations has enabled the mechanisms of water encroachment in gas-condensate reservoirs to be visualised at pressures above and below dewpoint, and has highlighted the differences between flow in this system and the more conventional three-phase flow processes. The continuity of condensate throughout the pore space results in its efficient displacement ahead of encroaching water. Condesate recovery is strongly affected by the rate of advancing water and the distribution of condensate in the pores, with the residual gas-condensate saturation being dependant on the water advancement rate and degree of pore heterogeneity. The extent of the isolation of residual gas-condensate pockets in pores determines the increase in residual hydrocarbon saturation required for gas remobilisation by depletion. This paper explains some ambiguities in the residual hydrocarbon and its remobilisation as recently reported in literature, and the results should assist in improving our understanding of gas-condensate recovery and hence in the management of gas-condensate reservoirs.

The Effect of Solids Concentration and Formation Characteristics on Formation Damage and Permeability Recovery

An experimental study has been made. to investigate the effect of solids concentration and fdtcr media on fluid loss and permeability recovery of cores. KClpolymer muds of different”barite concentrations and different types of core were used to perform the tests. Filtration tests showed that fluid loss increased as solids concentration” in the mud increased. Increasing the @ids cone.en.trati~n in the mud appems to improve perrneablhty recovery when the cores were backfhrshecf. However, high spurt 10SS and poor permeability recovery were observed if muds.. contairiliig” polymer materials were used without the addition of solid particles. Filtration and perrneabifity restoration are not orily affected by the sire, shape and solids concentration in the mud but also to the pore size distribution and core characteristics.. Detded observation using scanning electron microscope was used to identify the solids impairment at the core face. Therefore, to reduce formation damage and improve recovery, suitable size, shape and concentration of solids in the mud must be properly selected. .. ..=,.. . . .=–= References and illustrations at the end of paper. INTRO DUCT16N. .“ Forination damage and borehole filtratiori we very importznt esp’ecially in drilling and completion operations. Any filtrate lost and particle invasion into the exposed section adjacent to the .yeflbo~ will be a potenti@_source of damage. Irr some cases the fdtrate may react with me drilled formation and cause rn&chaoi@ instabuity to the borehole. Damage tlom mud solids is strongly, dependent on @e pore size ~: distribution of the formation, the particle size distribution in the drilling fluid and on the wellbore overbalance pressure. Inviiiori ..occrrrs with all muds during drilfirrg. However, it is possible tominimifi solids invasion and formation impairment by adding bridging material to the muds. Investigators I-3 have shown mat the bridging of pores by particles is required to Riitiate fiiter cake formation. This bridging material is chosen by matching its size to the foirnation rock . pore s]zes. A bridge maybe irriti&d when two large particles stat to move into an opening at the same time and lodge against each other. Other smaller paxticles may be bridge the openings between the larger, previously bridge particles. If the proper particle sizes are present, this process may contiriue until the openings become too small for any contained solids to penetrate. It is at this time that only the filtrate flows thrmrgh the ftiter cake.

Design of an effective gravel pack for sand control: a numerical approach

This paper provides useful guidelines for the selection of gravel for the prevention of sand migration. The authors suggest that in order to obtain satisfactory drainage patterns in offshore reservoirs from central platforms or templates in deeper water, the development wells have had to be drilled at angles between the vertical and the horizontal. Higher success rates in packing have been sought and it is likely that the effective placement of gravel in a deviated wellbore will become an essential part of the completion process for a large number of the offshore developments which at present are considered marginally economic.

A Numerical Approach to the Design of a Gravel Pack for Effective Sand Control in Deviated Wells

The process of gravel packing involves a substantial number of variables which must be specified by the operator. The relationship between the variables, especially for gravel packing in highly deviated wells, is not well understood. Further, the effective packing of perforations in deviated wellbores is critical to ensuring both a productive and stable gravel packed well. This paper reports on the development of a microcomputer based package which incorporates several numerical design models as options for the design of effective gravel packing in the screen/casing annulus and inside the perforations. Comprehensive testing of the model has indicated that the annular gravel packing process is controlled by not one but a number of parameters and thus a computer based prediction model is necessary. The packing of perforations is very difficult to accomplish with any great degree of success and is largely controlled by hole angle, perforation phasing and physical size characteristics rather than the transport controlling parameters such as viscosity, gravel size and leak off rate.

The Design and Optimisation of Gravel Packing Operations in Deviated Wells

Gravel packing is a widely applied technique for the control of sand. The increasing application of directional drilling both on and offshore has led to a number of completion difficulties. Gravel packing in deviated wells has for a long time caused considerable difficulties especially at hole angles above 40/sup 0/. This paper discusses the development and application of a computer based prediction package utilising both theeoretical principles and experimental data. The package named GRAVPACK has options available for the prediction of both annular and perforation packing efficiency for any specified set of conditions. The design of gravel packs is discussed with reference to the impact of specific wellbore parameters such as casing size, hole angle and required carrier fluid density upon packing efficiency. The sensitivity of annular packing efficiency to variable design parameters such as screen/tailpipe size, slurry flowrate, gravel concentration etc. is investigated. The packing of perforations in deviated wells is investigated with reference to perforation characteristics of length, diameter and phase angle. For the cases of annular and perforation packing comparison is made between the use of a high viscosity/concentration slurry technique and a low viscosity/concentration gravel packing system.