SHALE GAS RESERVE ESTIMATION

BY-Shruti Joshi(R8701210030)

Pranav Pal Singh(R8701210041)

Vivek Singh (R8701210044)

Three main steps involve-

Data gathering

and preparation

Performing natural fracture system

modelling and

simulation

Completing top-down intelligent reservoir

modelling.

1.Natural fracture system modelling and simulation-

Numerical model for naturally fractured gas reservoirs that permits the modelling of irregular flow paths, mimicking the complex system of interconnected natural fractures in a reservoirs. This type of natural fracture reservoir simulation permits a more accurate and realistic representation of fractured porous media when modelling fluid flow compared to the traditional deterministic formulations.

The mathematical model ‘decouples’ fluid flow in fractures and matrix, and solves a one-dimensional unsteady state flow problem in the matrix domain to compute the volumetric flow rates from matrix into fractures and wellbores.

2.Sensitivity analysis on reservoir and fracture properties-The objective of sensitivity analysis is to study

the impact of different parameter and identify the factors that have the most contribution to flow.

Sensitivity analysis is performed, with the purpose of scrutinising the influence of Initial reservoir pressure, matrix porosity, matrix permeability, net pay thickness and ARF(the hydraulic apertures of the fractures ) on flow behaviour.

3. History matched model-Upon completion of the sensitivity, analysis and careful

study of the impact of different parameters on production a new set of parameters were identified. This new set was used in history matching. The history matched model results in reliability of fracture network and history matched model.

4. Economic analysis-Economic analyses has been performed to investigate the

influence of the parameters such as initial reservoir pressure, natural fracture, and horizontal lateral length that have most contribution in flow on the Net Present Value of benefits from producing gas wells.

The same analysis has been performed on different horizontal lateral length (800, 1,000, 1,200, and 1,400 ft.) to show that the drilling horizontal wells are more favourable than drilling vertical well in Shale gas formation.

5. Top-down intelligent reservoir modelling-Top-down, intelligent reservoir modelling

starts with well-known reservoir engineering techniques such as decline curve analysis, type curve matching, and (single-well) production history matching as well as volumetric reserve estimation, and calculation of recovery factors. All these analyses are performed on individual wells.

Using statistical techniques, multiple production indicators (first three, six, and nine-month cumulative production as well as one, three, five, and ten-year cumulative gas production) are calculated.

Shale gas reserve estimationShale’s are geological rock formations rich in

clay and low in permeability. Gas shale’s have become an attractive target

because they represent a huge resource (500-780 TCF).

Estimation of contacted gas in place/ reserves in unconventional gas reservoirs is a problematic issue and the uncertainty associated with the estimate is relatively higher.

Shale gas reserve estimation is done by the following methods generally:

Total Organic CarbonVolumetric estimationDecline Curve Analysis

Total Organic Carbon1.Production: Organic production provides

the raw material upon which an ecosystem acts. Its primary proximate controls are the supply rates of solar energy, nutrients, and water.

2.Destruction: Oxidation and respiration component of destruction rate:

3.Dilution:Dilution of organic matter by material that is not hydrogen rich.

Population net growth relation indicating functional form of biogenic dilution processes:

4.Interaction of processes: Although organic-matter enrichment can be expressed as a relatively simple relation, it is quite complex in detail because of the interdependencies of the variables:

Organic-matter enrichment = Production – (Destruction + Dilution)

Volumetric Estimation:Calculation of reserve at initial stage in cubic ft. per

acre-foot by using well logs, core analysis data, bottom hole samples and subsurface maps.

Principle of Volumetric Methods- Volume x Porosity X saturations with hydrocarbon. G(in place gas) =A x h x Φ x (1 – Sw) x Pi x 1/zi x Tsc / Ti

where Zi is deviation factor at reservoir pressure and

temperature.Pi is reservoir pressure (abs.), Ti is 273° K + T°res C, Tsc

is 273° K + 15° C

Decline Curve analysis:Use of a family of rate time and cumulative

production time relations- exponential, hyperbolic and harmonic decline for estimation of gas in place for a variety of producing conditions.

The most common methods on the analysis of well performance data (particularly rate-time data) include the works of Arps .

Arps' empirical work suggests the use of a family of rate-time and cumulative production-time relations which can be assumed as valid for a variety of producing conditions for practical purposes.

The quadratic rate-cumulative relation is given as:

Summary:"Rate-cumulative production" and the "power-law

exponential" rate decline relations are used in conjunction to yield an integrated approach using only rate-time data.

Rate-cumulative production relation is incorporated into the procedure by making use of four plotting functions.

Power-law exponential rate decline is converted into a dimensionless form to obtain type curve solutions.

The procedure proposed in this work yields consistent contacted gas-in-place/reserves es timates. The uncertainty is significantly reduced if the integrated approach is used.

This methodology is well suitable for direct estimation of contacted gas-in-place/reserves in tight gas and shale gas reservoir systems.