Changes

==Problem prevention and correction==

==Problem prevention and correction==

[[:Image:Table1.png|Table 1]] summarizes potential rock fluid reactions based on knowledge of clays present, damage prevention, and corrective procedures (Kersey, 1986)<ref name=Kersey_1986>Kersey, D. G., 1986, The role of petrographic analyses in the design of non-damaging drilling, completion, and [[stimulation]] programs: Society of Petroleum Engineers Paper No. 14089.</ref>. Prevention is preferred and, when possible, is likely to cost less than correction.

[[:Image:able_dare-keelan-j-o-amaefule_rockwater-reaction_1.png|Table 1]] summarizes potential rock fluid reactions based on knowledge of clays present, damage prevention, and corrective procedures (Kersey, 1986)<ref name=Kersey_1986>Kersey, D. G., 1986, The role of petrographic analyses in the design of non-damaging drilling, completion, and [[stimulation]] programs: Society of Petroleum Engineers Paper No. 14089.</ref>. Prevention is preferred and, when possible, is likely to cost less than correction.

 

===Laboratory tests===

===Laboratory tests===

* Thin sections

* Thin sections

* X-ray diffraction

* X-ray diffraction

* Scanning electron microscopy (SEM)

* [[Scanning electron microscopy (SEM)]]

# Salinity-related tests

# Salinity-related tests

* Liquid [[permeability]]

* Liquid permeability

* Depth of damage studies

* Depth of damage studies

* [[Capillary pressure]]

* [[Capillary pressure]]

* Water shock

* [[Water shock]]

* Critical cation concentration

* Critical cation concentration

# Rate-related tests

# Rate-related tests

====Petrographic analysis====

====Petrographic analysis====

Petrographic analysis indicates the potential for [[permeability]] reduction by identifying types, amount, and location of clays and other minerals. (For details on petrographic methods, see the chapters on [[Thin section analysis]] and "SEM, XRD, CL, and XF Methods" in Part 5.)

[[Petrographic analysis]] indicates the potential for permeability reduction by identifying types, amount, and location of clays and other minerals.

====Salinity-related tests====

====Salinity-related tests====

Salinity-related tests furnish direct indication of rock-water interaction. They allow evaluation of damage induced by drilling, completion, workover, and injection fluids. Figure 1 illustrates results of a laboratory experiment to evaluate the reaction to reservoir rock with a proposed injection brine. [[Permeability]] was reduced to 20% of its original value after exposure to 20 pore volumes of proposed injected brine. Good reservoir management requires that injected volumes equal produced volumes; therefore, reduced injectivity results in reduced hydrocarbon production rates.

[[File:RWRFigure1.png|thumbnail|Liquid permability test indicating permeability reduction due to rock-liquid reaction.]]

Capillary (water retentive) properties of rocks are altered by rock-fluid reactions. Capillary curves before and after  

Salinity-related tests furnish direct indication of rock-water interaction. They allow evaluation of damage induced by drilling, completion, [[workover]], and [[injection fluids]]. [[:Image:RWRFigure1.png|Figure 1]] illustrates results of a laboratory experiment to evaluate the reaction to reservoir rock with a proposed injection brine. Permeability was reduced to 20% of its original value after exposure to 20 pore volumes of proposed injected brine. Good reservoir management requires that injected volumes equal produced volumes; therefore, reduced injectivity results in reduced hydrocarbon production rates.

exposure to extraneous fluids indicate if rock-fluid reaction has reduced pore sizes. If reduction occurs, retained water saturation is increased (Amaefule and<ref name=Amaefule_etal_1986>Amaefule, J. O., K. Wolfe, J. D. Walls, A. O. Ajufo, and E. Peterson, 1986, Laboratory determination of effective liquid [[permeability]] in low-quality reservoir rocks by the pulse decay technique: 56th California SPE Regional Meeting of the Society of Petroleum Engineers, Oakland, CA, April 2-4, [[spe:15149|SPE paper 15149]], p. 493-502.</ref>. (For more on [[capillary pressure]], see the chapter on [[Capillary pressure]] in Part 5.)

Capillary (water retentive) properties of rocks are altered by rock-fluid reactions. Capillary curves before and after exposure to extraneous fluids indicate if rock-fluid reaction has reduced pore sizes. If reduction occurs, retained water saturation is increased. <ref name=Amaefule_etal_1986>Amaefule, J. O., K. Wolfe, J. D. Walls, A. O. Ajufo, and E. Peterson, 1986, Laboratory determination of effective liquid permeability in low-quality reservoir rocks by the pulse decay technique: 56th California SPE Regional Meeting of the Society of Petroleum Engineers, Oakland, CA, April 2-4, [[spe:15149|SPE paper 15149]], p. 493-502.</ref>

When the source and composition of brine to be injected is unknown, water shock tests indicate potential rock damage and present a worse-case scenario. [[Permeability]] of the formation rock to a 0.51-M (3 wt. %) NaCl solution is followed by [[permeability]] to freshwater. Sensitive rocks will show [[permeability]] reduction. Rock-water reaction must be evaluated for all aqueous fluids introduced into the reservoir system. Critical salinity (cation concentration) below which damage occurs, as well as schemes to lower brine concentration stepwise so as to avoid clay damage, can be evaluated in the laboratory.

When the source and composition of brine to be injected is unknown, [[water shock tests]] indicate potential rock damage and present a worse-case scenario. [[Permeability]] of the formation rock to a 0.51-M (3 wt. %) NaCl solution is followed by permeability to freshwater. Sensitive rocks will show permeability reduction. Rock-water reaction must be evaluated for all aqueous fluids introduced into the [[reservoir system]]. Critical salinity (cation concentration) below which damage occurs, as well as schemes to lower brine concentration stepwise so as to avoid clay damage, can be evaluated in the laboratory.

====Rate-related tests====

====Rate-related tests====

The critical interstitial velocity at which [[permeability]] reduction due to fines migration is initiated can be determined in laboratory tests. These tests simulate the effect of high flow rates that exist near the wellbores of both injection and production wells. Muecke (1979)<ref name=Muecke_1979>Muecke, T. W., 1979, Formation fines and factors controlling their movement in porous media: Journal of Petroleum Technology, v. 31, p. 144-150.</ref> discusses factors controlling fines movement. These include fluids flowing, fines [[wettability]], and interfacial forces.

The critical interstitial velocity at which permeability reduction due to fines migration is initiated can be determined in laboratory tests. These tests simulate the effect of [[high flow rates]] that exist near the wellbores of both injection and production wells. Muecke (1979)<ref name=Muecke_1979>Muecke, T. W., 1979, Formation fines and factors controlling their movement in porous media: Journal of Petroleum Technology, v. 31, p. 144-150.</ref> discusses factors controlling fines movement. These include fluids flowing, fines [[wettability]], and interfacial forces.

Figure 2 illustrates laboratory data that established a critical flow velocity of 0.3 cm/sec. Beyond this rate, fines were mobilized that bridged at pore throats and resulted in reduced [[permeability]]. The pH of the effluent was monitored throughout the test. The constant pH value indicated that no chemical reaction was occurring between the rock and fluid and that viscous forces were the cause of the reduced [[permeability]].

[[File:RWRFig2.png|thumbnail|Critical velocity determination with pH monitoring]]

The critical flow velocity is normally obtained by testing a cylindrical sample, with flow parallel to the linear axis. The linear velocity can be scaled to the radial flow condition existing in the wellbore. The scaled data yield the maximum well flow rate in barrels per day that can be tolerated before fines bridging and loss of production rate occurs (Gorman et al., 1989)<ref name=Gorman_etal_1989>Gorman, I., C. Balnaves, J. Amaefule, D. Kersey, and D. Manning, 1989, Gravel packing in poorly lithified reservoirs: Laboratory systems approach to aid decision-making strategies: Society of Petroleum Engineers Paper No. 19477.</ref>. These data allow calculation of the radius of the [[permeability]] impaired zone and aid in sizing subsequent acid volumes required to clean up the impairment.

 

The critical flow velocity is normally obtained by testing a cylindrical sample, with flow parallel to the linear axis. The linear velocity can be scaled to the radial flow condition existing in the wellbore. The scaled data yield the maximum [[well flow rate]] in barrels per day that can be tolerated before fines bridging and loss of production rate occurs.<ref name=Gorman_etal_1989>Gorman, I., C. Balnaves, J. Amaefule, D. Kersey, and D. Manning, 1989, Gravel packing in poorly lithified reservoirs: Laboratory systems approach to aid decision-making strategies: Society of Petroleum Engineers Paper No. 19477.</ref> These data allow calculation of the radius of the permeability impaired zone and aid in sizing subsequent acid volumes required to clean up the impairment.

Test conditions should mirror the field condition under study. Thus, water injection tests should be made on reservoir rock specimens in which simulated injection brine is flowed in the presence of residual hydrocarbons. Oil or gas production tests should be made by flowing the appropriate hydrocarbon through the rock specimen with interstitial water present. Drag forces are proportional to both rate and viscosity; therefore, flowing fluid viscosities should also model reservoir values.

Test conditions should mirror the field condition under study. Thus, water injection tests should be made on reservoir rock specimens in which simulated injection brine is flowed in the presence of residual hydrocarbons. Oil or gas production tests should be made by flowing the appropriate hydrocarbon through the rock specimen with interstitial water present. Drag forces are proportional to both rate and viscosity; therefore, flowing fluid viscosities should also model reservoir values.

 

Changes in pH indicate fluid-fluid or rock-fluid reactions; therefore, monitoring of injection and produced water pH should be an integral part of any critical velocity determination. In addition, effectiveness of clay stabilizers should be evaluated as an extension of the critical velocity measurement.

Changes in pH indicate fluid-fluid or rock-fluid reactions; therefore, monitoring of injection and produced water pH should be an integral part of any critical velocity determination. In addition, effectiveness of clay stabilizers should be evaluated as an extension of the critical velocity measurement.