--> --> Advances in Reservoir Quality Assessment of Tight-Gas Sands - Links to Producibility, by Robert Klimentidis and Joann E. Welton; #40395 (2009).
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Advances in Previous HitReservoirNext Hit Quality Assessment of Tight-Gas Sands - Links to Producibility*

Robert Klimentidis1 and Joann E. Welton1

 

Search and Discovery Article #40395

Posted March 16, 2009

 

*Adapted from extended abstract prepared for presentation at AAPG Annual Convention, San Antonio, Texas, April 20-23, 2008

 

1ExxonMobil Research, Houston, TX ([email protected]; [email protected])

 

Abstract

 

Quantification of Previous HitporosityNext Hit types and sizes coupled with in-situ Previous HitreservoirNext Hit capillary pressure data allows one to estimate potential hydrocarbon pore volume in a hydrocarbon transition zone. Integration of this data with economic gas rate production and Previous HitreservoirNext Hit quality data (such as Previous HitsandstoneNext Hit compositional and textural trends on a field or basin scale) can provide a tool to evaluate Conventional vs. Tight-Gas zones in a prospect.

Three modes of Previous HitporosityNext Hit volumes can be described in sandstones: 1) movable or maximum potential hydrocarbon pore volume usually associated with intergranular Previous HitporosityNext Hit; 2) clay-bound water volume associated with detrital and diagenetic clays; and 3) other bound-water typically located in secondary pores within partially dissolved minerals (i.e., feldspars) and in detrital lithics sedimentary, volcanic, metamorphic) (Figure 1 ).

The two main Previous HitporosityNext Hit types found in sandstones are primary intergranular Previous HitporosityNext Hit and secondary microporosity. Primary intergranular Previous HitporosityNext Hit occurs between detrital grains. Secondary Previous HitporosityNext Hit is located in partially dissolved minerals, microporous detrital grains and matrix, and various diagenetic mineral cements such as clay minerals (chlorite, kaolinite, illite/smectite, illite, etc.) (Figure 2) . Differentiation and quantification of the various Previous HitporosityNext Hit types is an essential step in understanding and Previous HitpredictingNext Hit the producibility of tight-gas reservoirs. MicroQuant is a SEM/BSE technique which has been developed to quantify secondary microporosity from petrographic thin sections (Figure 3 ).

Conventional gas reservoirs consist predominantly of primary intergranular Previous HitporosityNext Hit with large pore-throat sizes and varying amounts of secondary Previous HitporosityNext Hit (Figure 4). In contrast, tight-gas reservoirs (i.e., a Previous HitreservoirNext Hit which requires artificial stimulation to produce at economic rates) consist predominantly of secondary Previous HitporosityNext Hit with pore-throat sizes below 1 micron in diameter (Figure 4 ).

Pore-throat size distribution is a key control on properties such as permeability, water saturation, producible pore volume, and producibility potential (e.g., hydrocarbon flow rates and cumulative production). The ability to characterize and quantify pore types and sizes based on mineralogical trends in a stratigraphic framework within a basin allows one to build a predictive Previous HitreservoirNext Hit quality spatial model (Figure 5 ). The integration of rock quality data, pore-throat size distribution, and economic gas rates can be mapped to differentiate Conventional vs. Tight-Gas reservoirs in a basin or field. This protocol can also be used to locate better Previous HitreservoirNext Hit quality intervals (“sweet-spots”) for optimized field development.

 

 

Figure Captions 

 

Figure 1. Three modes of fluid saturation.

 

 

Figure 2. Primary vs. secondary Previous HitporosityNext Hit.

 

 

Figure 3. Quantification of microporosity using thin section and SEM/BSE.

 

 

Figure 4. Mercury Injection Capillary Pressure tests (MICP) are used to link pore-throat size distribution, petrographic analysis, and potential maximum hydrocarbon pore volume.

 

 

Figure 5. Tight Gas Resource Map. Detailed Previous HitreservoirNext Hit characterization using core, logs, and production data confirmed the primary controls on Previous HitreservoirTop quality. This information was then used to create a map which differentiates Conventional vs. Tight-Gas resources to optimize field development.