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Research Papers: Petroleum Engineering

Insights of Wormhole Propagation During Carbonate Acidizing: A Comparison Between Constant Injection Pressure Versus Constant Volumetric Rate

[+] Author and Article Information
Ahmed M. Gomaa

Baker Hughes Inc.,
11211 FM 2920 road,
Tomball, TX 77379

Andrea Nino-Penaloza, Jennifer Cutler, Saleem Chaudhary

Baker Hughes Inc.,
11211 FM 2920 road,
Tomball, TX 77379

Contributed by the Petroleum Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received January 8, 2016; final manuscript received February 25, 2018; published online June 12, 2018. Assoc. Editor: Daoyong (Tony) Yang.

J. Energy Resour. Technol 140(10), 102906 (Jun 12, 2018) (10 pages) Paper No: JERT-16-1020; doi: 10.1115/1.4039443 History: Received January 08, 2016; Revised February 25, 2018

Acidizing of carbonate reservoirs is a common technique used to restore and enhance production by dissolving a small fraction of the rock to create highly conductive channels. Literature review reveals that most acidizing studies are focused on acid injection at a constant volumetric rate (CVR) instead of at a constant injection pressure (CIP). Therefore, the primary objective of the present work is to investigate the benefits and recommended applications of each technique. The study analyzes dissolution patterns and wormhole propagation rate. A coreflood study was conducted using different Indiana limestone cores to assess both techniques. Additionally, a two-dimensional (2D) wormhole model was used to mathematically describe the acidizing phenomena. The algorithm is based on a 2D radial flow system that iterates time to quantify wormhole propagation and injection rate. Wormhole velocity is calculated by an empirical laboratory model that depends on two parameters measured from core flow testing. Therefore, the algorithm captures the essential physics and chemistry of the acid reaction in a carbonate porous medium. The study confirmed that conical, wormhole, and branched types of acid dissolution patterns exist for both techniques (CVR or CIP). Unlike in the CVR technique, dissolution patterns during the CIP technique can change and tend toward a branched dissolution regime. The CIP technique required a lower acid volume to achieve a breakthrough in the conical dissolution regime and a higher acid volume to achieve a breakthrough in the branched dissolution regime compared to the CVR technique. In a dominant wormhole pattern, both techniques required nearly the same acid volume for a breakthrough. A computed tomography (CT) scan confirmed that the CIP technique developed a uniform wormhole at a low initial injection rate. For the CIP technique, the acid injection rate increased exponentially with the volume of the acid injected. The CIP technique is recommended for a low-permeability reservoir where acid injection at a high rate is not possible to avoid face dissolution wormhole patterns. On the other hand, the CVR technique is recommended for a medium—to the high-permeability reservoir where high acid injection rate can be achieved.

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Figures

Grahic Jump Location
Fig. 2

The acid volume to breakthrough as a function of acid injection for 15 wt % HCl injected at CVR, T = 75 °F

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Fig. 3

The increase in the normalized acid injection rate across cores 4, 5, and 6 while injecting 15 wt % regular HCl at CIP with initial rates of 2.05 × 10−5, 3.53 × 10−5, 1.48 × 10−4 ft3/min, T = 75 °F

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Fig. 4

The acid volume to break through as a function of initial acid injection for 15 wt % HCl injected at CIP, T = 75 °F

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Fig. 5

Computed tomography scan for core 1 after acidizing with 15 wt % HCl at CVR of 1.77 × 10−5 ft3/min

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Fig. 6

Computed tomography scan for core 2 after acidizing with 15 wt % HCl at CVR of 3.53 × 10−5 Ft3/min

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Fig. 7

Computed tomography scan for core 3 after acidizing with 15 wt % HCl at CVR of 1.77 × 10−4 ft3/min

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Fig. 8

Computed tomography scan for core 4 after acidizing with 15 wt % HCl using CIP at an initial rate of 2.05 × 10−5 ft3/min

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Fig. 9

Computed tomography scan for core 5 after acidizing with 15 wt % HCl using CIP at an initial rate of 3.53 × 10−5 Ft3/min

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Fig. 10

Computed tomography scan for core 6 after acidizing with 15 wt % HCl using CIP at an initial rate of 1.48 × 10−4 Ft3/min

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Fig. 11

Effect of acid injection rate method (CVR versus CIP) on acid volume to breakthrough as a function of initial interstitial velocity,15 wt % HCl

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Fig. 12

The bottomhole pressure, surface treatment pressure, and treatment injection rate for case 1

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Fig. 13

The final skin factor and wormhole front length as a function of zone index (depth), case 1

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Fig. 14

The bottomhole pressure, surface treatment pressure, and treatment injection rate, case 2

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Fig. 15

A comparison of the post-treatment skin and wormhole front length between the two case study scenarios: CVR (case 1) and CIP (case 2), region III

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Fig. 16

A comparison of the Vi/Viopt for three zones at the heel, middle, and toe end of the well, under the two case study scenarios: CVR (case 1) and CIP (case 2), region III

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Fig. 17

The bottomhole pressure, surface treatment pressure, and treatment injection rate for case 3

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Fig. 18

The bottomhole pressure, surface treatment pressure, and treatment injection rate for case 4

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Fig. 19

A comparison of the post-treatment skin and wormhole front length between the two case study scenarios: CVR (case 3) and CIP (case 4), region II

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Fig. 20

A comparison of the Vi/Viopt for three zones at the heel, middle and toe end of the well, under the two low-permeability case study scenarios: CVR (case 3) and CIP (case 4), region II

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