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Research Papers: Petroleum Engineering

New Formulation for Sandstone Acidizing That Eliminates Sand Production Problems in Oil and Gas Sandstone Reservoirs

[+] Author and Article Information
Mohamed Mahmoud

Department of Petroleum Engineering,
King Fahd University of Petroleum & Minerals,
Dhahran 31261, Saudi Arabia
e-mail: mmahmoud@kfupm.edu.sa;
mohnasreldin80@gmail.com

Contributed by the Petroleum Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received October 22, 2016; final manuscript received March 5, 2017; published online March 30, 2017. Assoc. Editor: Arash Dahi Taleghani.

J. Energy Resour. Technol 139(4), 042902 (Mar 30, 2017) (11 pages) Paper No: JERT-16-1416; doi: 10.1115/1.4036251 History: Received October 22, 2016; Revised March 05, 2017

The sandstone rocks' integrity and consolidation may be highly affected by the type and the strength of the stimulation fluids. Strong acids such as HF/HCl impair the rock consolidation. The reduction in the sandstone rock consolidation will trigger the sand production. Sand causes erosion of downhole and surface equipment especially when it is produced with high gas flow rates. In this study, gentle stimulation fluids for sandstone that consists of chelating agents and catalyst were proposed. The chelating agents are diethylene triamine penta acetic acid (DTPA) and ethylene diamine tetra acetic acid (EDTA). This is the first time to introduce a catalyst (potassium carbonate) in sandstone acidizing. Potassium carbonate was found to work as a clay stabilizer and catalyst that enhances the dissolution of chlorite clay mineral in the sandstone rock. The objective of introducing the catalyst is to enhance the solubility of the insoluble minerals such as chlorite clay minerals. The change in the mechanical properties of sandstone rocks (Bandera and Berea) was evaluated. The possibility of the formation damage after using seawater-based chelating agents was investigated and compared to HF/HCl mud acid. Coreflooding experiments were conducted to evaluate the effect of these fluids on the rock integrity. Computed tomography (CT) scanner was used to assess the formation damage. Different models were used to predict the sand production possibility after the stimulation with chelating agent/catalyst, and this was compared to the HF/HCl mud acid. The results showed that the permeability of sandstone core increased after acidizing. The reduction in CT-number after acidizing confirmed that no formation damage occurred. Rock mechanics evaluation showed no major changes occurred in the rock moduli and no sand production was observed. The model results showed that using chelating gents to stimulate Berea (BR) and Bandera (BN) sandstone cores did not cause sand production. Applying the same models for cores stimulated by HF/HCl acids indicated high possibility of sand production. The addition of potassium carbonate to DTPA chelating agents enhanced the chlorite clay mineral dissolution based on the inductively coupled plasma (ICP) analysis. Potassium carbonate as a catalyst did not affect the sandstone integrity because it only enhanced the dissolution of chlorite clay minerals (selective dissolution) and did not affect the solubility of carbonate minerals which are the primary cementing materials in the sandstone cores. A new dimensionless number was developed that describes the relation between the number of pore volumes (PVs) contacted the rock and the radial distance from the wellbore.

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References

Figures

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Fig. 1

Chelating agent used in the oil and gas well stimulation

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Fig. 2

Effect of potassium carbonate in the stimulation of Berea and Bandera sandstones with high pH chelating agents

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Fig. 3

Effect of catalyst on the iron concentration (chlorite dissolution)

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Fig. 4

Permeability improvement ratio of Berea and Bandera sandstones after injecting six and ten pore volumes of EDTA solution (pH = 11) at 250 °F at injection rate 5 cm3/min

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Fig. 5

Permeability improvement ratio of Berea and Bandera sandstones after injecting six and ten pore volumes of DTPA solution (pH = 11) at 250 °F at injection rate 5 cm3/min

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Fig. 6

Schematic illustration shows a damage radius of 3 ft in a sandstone reservoir and radial distance of r

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Fig. 7

Number of pore volumes injected as a function of the radial distance from the wellbore. The Y-axis represents the number of pore volume that contacts the rock at the end of injection at radial distance 3 ft from the wellbore of a radius of rw = 0.5 ft.

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Fig. 8

Effect of DTPA, EDTA, and mud acid on the Young's moduli of Berea and Bandera cores

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Fig. 9

Change of Young's modulus with core permeability after stimulation by 20 wt % DTPA chelating agent. Berea sandstone cores were used here at the same experimental conditions.

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Fig. 10

Effect of stimulation fluid type on the permeability enhancement and Young's modulus of Berea sandstone cores

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Fig. 11

Effect of injected pore volumes of EDTA, DTPA, and mud acid on the Poisson's ratio of Berea and Bandera sandstone cores

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Fig. 12

Effect of injected pore volumes of EDTA and DTPA on the Bulk moduli of Berea and Bandera cores

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Fig. 13

Predicting sand production using shear modulus to bulk compressibility ratio after acidizing Berea and Bandera cores using EDTA, DTPA, and mud acid solutions

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