Chemical Injection Related Sand Failure: An Experimental Investigation

Gbenga Folorunso Oluyemi

6th European Sand Management Forum

Wednesday 26th – Thursday 27th March 2014 Aberdeen Exhibition and Conference Centre Aberdeen

Introduction

• Evaluation of geomechanical properties of reservoir formation

– a key requirement in sand production related field optimization especially in fields where there is an active programme of chemical injection to enhance production (Oluyemi et al., 2010).

• Why is this so? – reason not far fetched!!!!

• Chemical interaction between the formation rock and the chemical species in injected fluid.

– Similar mechanism to chemical weathering of exposed rock??? Maybe…maybe not???

The million dollar question??

• But do we as an industry consider the likely effects of these chemicals in the implementation of geomechanical and failure evaluation of formation that have had substantial contact with chemical application????

• The answer is probably no? – we don’t even think of it as being important!!!

• Even if some are doing it, they definitely constitute a small section of the industry???

So what is the current knowledge….???

Formation damage effects of chemical inhibitor application

• We are very clear about the formation damage aspects of chemical inhibitors when applied to carbonate reservoir formation

– dissolution of carbonate material which may lead to sand failure and production especially if the fabric of sand is held together by carbonate cement.

– dissolution of carbonate minerals would also result in a localised increase in calcium cation concentration and pH which could in turn result in the precipitation of an inhibitor / cation precipitate or pseudo scale.

So what is the current knowledge….???

Evidence from previous work….

• Engebretson et al., 1997 - investigated the effect of chemicals such as dodecyltrimethyl ammonium bromide (DTAB), polyethylene oxide (PEO), and aluminium chloride (AlCl3) on the strength of sandstone.

• Their aim was to establish fundamental knowledge which can be used in the optimization of chemically assisted fracturing.

…and what are the issues???

• The issues with Engebretson et al., 1997:

– the study was limited in scope to static tests

– chemicals used in the study have totally different chemistries from the common oilfield chemicals.

• So where do we go from here?

– dynamic testing to capture failure effects of chemical under flow conditions…and perhaps using a range of oilfield chemicals

Approach

• The current work investigates experimentally, under dynamic conditions, any likely effects of scale inhibitors on the geomechanical strength and sand production potentials of soft Clashach rock analogous to unconsolidated reservoir rock.

• Based on the analysis of the experimental results, conceptual failure models were also formulated for describing the chemical inhibitor-formation rock interaction.

Experimental set-up and materials

• Coreflood rig with a pressure rating of 100 bar absolute line pressure and 50 psi differential pressure

• Hassler-type core-holder with a pressure rating of 5000 psi.

• Malvern Mastersizer 2000 - for grain size distribution measurement

• Vacuum filter pump with maximum pressure rating of 20 bar.

• Programmable pump with a working pressure of 100 bar

SEM

EDAX scan

Two identical cores A & B – identical in mineralogies, grain size distributions and strength????

Sub-rounded quartz grains and high traces of Si & O2

Injected fluids

• Brine – laboratory simulated brine; filtered through 45 micron filter papers to exclude fines

• A stock of 5% phosphonate scale inhibitor (PTEMP) solution prepared in brine.

Experimental implementation

• Stage 1 – Static saturation of Clashach cores

• Stage 2 – Dynamic saturation of Clashach cores and measurement of key petrophysical properties

Brine injection into the cores A and B at the rate of 1 ml/min; porosity and permeability of both cores also measured at this stage

• Stage 3 – Chemical Inhibitor injection into core A; inhibitor injection at the rate 0.25 ml/min

Cores A & B: porosity and permeability

Striking similarity in the values of porosity and permeability of the two cores. By inference, flow behaviour should be similar to a reasonable extent

Static tests

Comparison of grain size distribution of the original brine and effluents from Cores A and B

1. Similar grain size distribution

profiles for original brine and effluent brine from cores A and B

2. d10, d50, and d90 values of sand very close.

3. No evidence of grain particle in effluents

4. This is an indication that the brine had no detrimental physical or chemical effects on the grain fabric.

Dynamic test – brine injection

Comparison of grain size distribution of the original brine and effluents from Cores A and B

1. Similar grain size distribution profiles for original brine and effluent brine from cores A and B

2. d10, d50, and d90 values of sand very close.

3. No evidence of grain particle in effluents

4. This is an indication that the brine had no detrimental physical or chemical effects on the grain fabric.

Dynamic test –Failure effects of chemical injection

Comparison of grain size distribution of the original brine and effluents from Cores A and B

1. Significant difference in grain size distribution profiles for original brine and effluent brine from cores A but not for core B

2. Significant increase in d10, and d50 values of sand in core A effluent.

3. Evidence of grain particle in core A brine effluents

4. This is an indication that additional grain particles were introduced to core A effluent.

SEM - Failure effects of chemical injection

Before chemical injection

After chemical injection

Evidence from SEM

1. Evidence of fine-grained mineral agglomeration - formed alteration of the constituent minerals in core A (chemical injection)

2. No such alteration feature is seen in core B (no chemical injection) and of course in cores A and B (brine injection)

Strength of unconsolidated sands

• Unconsolidated sands are naturally very ‘soft’ and so have poor geomechanical strength. The major stabilizing factors for this type of sands include:

– The strength derived from capillary bonding – this furnishes cohesive strength (Han et al., 2002)

– The strength due to cementatious materials and mechanical attributes of sand – this furnishes mechanical strength (Han et al., 2002; Han and Dusseault, 2002; Papamichos et al., 1997)

Conceptual physico-chemical models

• Excessive pressure differential or drawdown – pore throat blockage by materials produced from chemical reaction between injected chemical and formation water.

• Geomechanical weakening – cement disintegration or weakening resulting from reaction between the injected chemical species and grain cement.

• Breakdown in cohesive strength – breakdown in capillary bonding resulting from alteration of the formation interfacial tension by the injected chemical specie; wettability alteration.

Conclusions

• Conceptual physico-chemical failure models for analysing inhibitor-formation interaction are proposed in this work.

• Laboratory evidence provided suggests that application of chemical inhibitor can have detrimental effects on the reservoir formation,

• These effects may lead to physically and chemically induced failure, and release and production of sand with the fluid streams.

• Further numerical and laboratory work are recommended to confirm the proposed physicochemical models.

• More importantly, this study has shown the need to integrate geochemical and geomechanical tests for production and reservoir management purposes

Acknowledgements

• The work on which this presentation is based was partly funded via IDEAS Short Funding initiative (IDEAS is one of the three themed research institutes at RGU)

• The work has also been published in Petroleum Science and Technology:

– Oluyemi, G. F. “Conceptual Physicochemical Models for Scale Inhibitor-Formation Rock Interaction.” Petroleum Science and Technology, 32(3): pp 253–260, 2014

References

• Engebretson, R. R., VonWandruszka, R., Seto, M., Nag, D. K., Vutukuri, V. S., and Katsuyama, K. (1997). Effect of chemical additives on the strength of sandstone. Int. J. Rock Mech. Min. Sci. Geomech. 34:691.

• Han, G., and Dusseault, M. B. (2002). Quantitative analysis of mechanism for water-related sand production. SPE 73737, International Symposium & Exhibition on Formation Damage Control, Lafayette, Louisiana, February 20–21.

• Han, G., Dusseault,M. B., and Cook, J. (2002).Quantifying rock capillary strength behaviour in unconsolidated sandstones. SPE/ISRM 78170, SPE/ISRM Rock Mechanics Conference, Irving, Texas, October 20–23.

• Oluyemi, G., Oyeneyin, M. B., and Macleod, C., (2010). UCS neural network model for real time sand prediction. Int. J. Eng. Res. Africa 2:1–13.

• Papamichos, E., Brignoli, M., and Santarelli, F. J. (1997). An experimental and theoretical study of a partially saturated collapsible rocks. Mech. Cohesive Frict. Mater. 2:1–28.