Permeability prediction in tight gas reservoirs

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Development of successful exploration and production strategies of tight gas reservoirs require a good insight in the (local) porosity-permeability distribution. Tight gas reservoirs are characterized by an exceptionally low permeability, which will critically depend on several factors such as depositional environment, diagenesis, and reservoir connectivity. TNO is building a quick screening tool that predicts porosity-permeability on the basis of rock type, burial history, lementation and tectonic stress regime. The tool will be integrated in basin modeling software in order to investigate typical porosity-permeability evolution of key stratigraphic units for realistic basin formation scenarios. Results are evaluated against porosity-permeability predictions based on geological modeling in a case study of a well-characterized tight gas reservoir. The tool can be used to improve predictions of the spatial distribution of porosity-permeability in hydrocarbon reservoirs, thereby helping in optimizing completion strategies in problematic gas systems.

WorkflowThe workflow aims at improving predictions of the spatial

distribution of porosity-permeability within tight gas reservoirs. The

workflow is particularly useful for areas where conventional methods

of predicting porosity-permeability are difficult to use due to a lack of

data. The following activities are performed:

• Developingatoolthatpredictstheevolutionofporosity-

permeability during diagenesis.

• Rocktypingtoclassifytypicalrocktypesintermsofproperties

that are required as input for the tool.

• Integrationofthetoolinbasinmodelingtoinvestigateporosity-

permeability evolution for typical burial histories.

• Evaluationoftoolpredictionsinatightgasreservoircasestudy.

TNO Built Environment and GeosciencesGeological Survey of the Netherlands is the central geoscience centre in the Netherlands for information and research to promote the sustainable management and use of the sub-surface and its natural resources.

TNO Built Environment and GeosciencesGeological Survey of the Netherlands

Princetonlaan 6PO Box 800153508 TA UtrechtThe Netherlands

T +31 30 256 46 00F +31 30 256 46 05E info-geoenergy@tno.nl

tno.nl

Exploration

Porosity-permea- bility prediction tool

The tool predicts the evolution of porosity-

permeability of reservoir rocks over geo-

logical time by modeling compaction and

cementation during diagenesis. As a base

case, compaction by grain fracturing and

solution-precipitation processes in a closed

system (mass balance) is modeled. Data from

experiments and field cases are combined

with discrete element models to model these

processes for the full range of relevant condi-

tions and compositions. The base case can be

extended to include other diagenetic proc-

esses, such as illite cementation, in situations

where these processes play an important role

and data is available. The tool requires rock

properties, pressure-temperature-time paths,

and stress conditions of rocks during burial

as input. The input is provided by a combina-

tion of rock typing and basin modeling.

Rock typingRock typing is performed to obtain a classifi-

cation of rock types with characteristic rock

properties that are linked to depositional

environment. Rock properties, such as clay

content, grain size distribution, and pore

throat geometry can be used as input for

the porosity-permeability prediction tool. By

running the tool for different rock types and

burial histories, the distribution of poros-

ity-permeability within stratigraphic units

and the potential for developing tight gas

reservoirs can be determined.

Basin modelingRealistic scenarios for the formation of sedi-

mentary basins are run using state-of-the-

art basin modeling software to investigate

typical burial histories of rocks. Pressure-

temperature-time paths and stress conditions

associated with these burial histories are

used as input for the porosity-permeability

tool. By combining basin modeling and rock

typing, the tool can be used to determine

the evolution of porosity-permeability for a

specific rock type and burial history.

Case studyPorosity-permeability predictions of the tool

are evaluated using a well-characterized case

study of (potential) tight gas reservoirs. An

example could come from the offshore Rot-

liegendes gasfields, NW of the Netherlands.

If information on the spatial distribution of

sedimentary facies is available, the tool can

be used in combination with rock typing

and basin modeling to predict the spatial

distribution of porosity-permeability. The

predictions are compared with porosity-per-

meability maps that are produced using cor-

relation of well logs, petrophysical analysis

of rocks, and geological modeling of facies

distribution.

Further InformationFor more information on porosity-permeabil-

ity prediction in tight natural gas reservoirs,

please contact us.