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Comprehensive and Integrated Research to Develop Predictive Models for

Shale Oil and Gas Reservoirs in Texas

The Crisman Institute for Petroleum Researchand

The Berg-Hughes Center for Petroleum and Sedimentary Systems

Outline• Hydraulic Fracturing Issues• Fracture Propagation Models• Propagating Multiple Fractures• Fracture ‘system’ input into Reservoir Simulators (Field

Example)• Fracture Fluids• Fracture Conductivity• Fracture Diagnostics by DTS measurements• Summary

Hydraulic Fracturing – Outstanding Issues

• How do you determine the optimal number of stages?• How do you determine the optimal number of clusters?• How do you determine the optimal fluids and proppants?• How many rock layers do we need in our fracture design models?• What is the best model to design and analyze fracture treatment

data?• What do we know about re-fracture treatments?• Can we monitor flow back data to learn about the fractures?• Can we run well tests to learn about the fractures?

The modeling dilemma• We have two data sets and two models

• One data set consists of the fracture treatment data• A second data set consists of production and pressure data

• We have one reservoir description that must be• used in the fracture design model to match the fracture

treatment data and• used in reservoir model to match the production data

• If the same reservoir description does not work in both models, then

• The reservoir description is not correct or• One or both models do not accurately depict what is going on

downhole

Fracture propagation issues• Number of clusters taking fluid at what injection rate?• How many fractures are being propagated

simultaneously?• What are values of rock mechanical properties that

allows us to propagate dozens of fractures in a single wellbore and pump away millions of pounds of proppant?

• How can we model not only created fracture dimensions but also propped fracture dimensions?

• Can we tie microseismic measurements to fracture propagation?



Fracture Propagation Models• For this research, we are mainly concerned with fracturing

horizontal wells with multiple stages and multiple perforation clusters

• We will use complete data sets with as much information as possible in our fracture propagation models

• We will evaluate commercial models with the data sets and build new code to better model what is going on in the field

• We will develop theory and practical computer code to better describe fracture propagation in shale reservoirs

• We will also look at fracture fluid and proppant transport issues

Fracture software for unconventional reservoirsMangrove: UFM, Wiremesh, planar 3D

MFRAC: Elliptical orthogonal fracture geometry represents complex fracture geometry

GOHFER: model longitudinal and transverse multiple fractures, no NF

StimPlan: Visualisation of microseismic data and DFN for NF

FracPro: Pseudo 3D model and fracture monitoring

8

Fracture software for unconventional reservoirs

Meyer et al., 2011

GOHFER

Mangrove

Stimplan



Well 1

Well 2

Natural fractures

What causes complex fracture geometry?

2. Heterogeneity • Pre-existing natural

fractures • Bedding layers

1. Fracture interaction • Between stages • Between horizontal

wells

11

Multiple Fracture Propagation

1) What mechanisms dominate multiple fracture propagation?

2) What are characteristics of multiple fracture geometry? 3) How to improve effectiveness of stimulation

treatments?

12

Young’s Modulus for Layered SystemMultiple layers in reservoir

• Effects of natural fractures and layers• Overestimate Young’s Modulus (E) ??

Core experiment

Effect of E on Multi-fracture PropagationFour fractures propagating simultaneously in a stageE1 = 6.53×106 psi

Twofold exaggeration of x-axis scale

Induced stress in σxx, psi

Effect of E on Multi-fracture PropagationFour fractures propagating simultaneously in a stageE3 = 6.53×105 psi

Twofold exaggeration of x-axis scale

Induced stress in σxx, psi

Fracture Propagation in a Naturally Fractured Reservoir

Four fractures propagate simultaneously in a single stage

• Fracture width is restricted on the NF segments • Geometry of fractures is not symmetry



Various diagnostic methods• Microseismic image• Tracer • Production data analysis• Tiltmeter• Temperature logs • Net pressure analysis

How to characterize complex fracture geometry?

18

From Fracture Model to Reservoir Model –a field example• Two wells drilled parallel• Detail measurements of flow rate and pressure were

made• Interference was seen during treatment and during

production• Microseismic was available • Tried to model production pressures while honoring

microseismic• Resulting fracture description very surprising

BH Pressure Gauge data in Well 2H

Frac Stage #

Initial BHP at start of frac

Final BHP at end of frac

Delta Pressure

(psi) (psi) (psi)1 3950 4003 532 3999 4070 713 4060 4234 1744 4130 4311 1815 4282 4600 3186 4344 4390 467 4340 4312 -28

TABLE 2 - INITIAL AND FINAL BHP VALUES IN WELL 2H DURING THE FRACTURE COMPLETION OF WELL 1H

Pressure increases in Well 2H during the completion of

Well 1H

Integrating MSM and BH Pressure Gauge

Import Microseismic Events into Reservoir Model

Reservoir Model Grid – Fractures based on SRV

SRV Model Does Not Honor Degree of Communication

SRV based model does not honor communication between wells.

Linear Fracture Model - Fracture Conductivity Distribution

Linear Fracture Model Does Honor Degree of Communication

Time (Date)

Wel

l Hea

d Pr

essu

re (p

si)

2009-112009-122010-12010-22010-32010-42010-52010-62010-72010-82010-90

1,000

2,000

3,000

4,000Communication between laterals is being honored.



Fracture Fluids• The choice of the fracturing fluid is important• Gel fluids carry proppant but do not clean up in many cases• Water fracs clean up better than gels but cannot transport

proppant• Apparently clean up is more important than proppant

transport since many companies find water frac wells are better initially

• We need to evaluate ultimate recoveries to be sure which fluid system is optimum

• What we really need is a better fluid – one that transport proppant but will break with little or no yield stress and low viscosity



Fracture Conductivity• Many wells are fracture treated with water fracs and

proppant transport is a real issue• The distribution of the proppant is still a large unknown• With narrow fractures and low viscosity fluids, the

proppant concentration in the fracture is usually very low

• When water reacts with the rock, the proppants can embed and the fracture conductivity may decrease substantially

• More research on increasing fracture conductivity is needed

Experimental Procedure2. Coat samples 3. Place

proppants

4. Mod. API cell 5. Measurement

1. Induce fracture

6. Analysis

Con

duct

ivity

(md-

ft)

Clo

sure

str

ess (

psi)

Time (min)

2.5”

2.5”

1”

Conductivity Measurement

Rock Mechanical Property Measurement

Unpropped and Propped Conductivity – Barnett Shale

0.1

1

10

100

1000

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Frac

ture

Con

duct

ivity

(md-

ft)

Closure Stress (psi)

No proppant 100 mesh, 0.10 lb/ft²

0.1

1

10

100

1000

0 500 1000 1500 2000 2500 3000 3500 4000 4500Frac

ture

Con

duct

ivity

(md-

ft)

Closure Stress (psi)

Unpropped Conductivity ComparisonFL2, Fayetteville

Eagle Ford

FL3,Fayetteville

Barnett

X Bakken No. 5X Bakken No. 6X Bakken No. 8

Conductivity Behavior

0.1

1

10

100

1000

0 1000 2000 3000Mea

sure

d Co

nduc

tivity

[mD

-ft]

Closure Stress [psi]

Magnitude of initial conductivity is dominated by surface topography

0.1

1

10

100

1000

0 1000 2000 3000 4000Mea

sure

d Co

nduc

tivity

[mD

-ft]

Closure Stress [psi]

Conductivity decline rate is controlled by mechanical properties



Using Downhole Temperature Data to Locate Hydraulic Fractures

Temperature profile at the start of Stage 3 injection

Stage 1

Stage 2

Fracture Locations Identified by Temperature

SPE 170874 • J. Cui, D. Zhu and M. Jin

Fracture Flow Distribution Interpreted from Temperature

(a) τ (hr1/2) (b) pressure (psi)

(c) temperature (°F) at one month (d) temperature (°F) at one year

Temperature Predicted for Complex Fracture System by Fast-Marching Method



Summary• We need to validate fracture propagation models with

fracture treatment data, microseismic measurements and production models

• We need to develop better models to incorporate layers, bulk rock properties and propagation of multiple fractures in multiple wells

• We need to develop better fracturing fluids• We need to better understand proppant transport and

conductivity• We need to determine how to incorporate fracture

treatment calculations into reservoir models

Documents

Comprehensive and Integrated Research to Develop ... · PDF fileComprehensive and Integrated Research to Develop Predictive Models for ... StimPlan: Visualisation of ... • Net pressure