Acid Fracturing or Proppant Fracturing in Carbonate Formation? A Rock
Mechanics View

Abass, Hazim; Al-Mulhem, Abdulrahman; Alqam, Mohammad H.; Khan, Mirajuddin

doi:10.2523/102590-ms

Cited by 23 publications

(10 citation statements)

References 6 publications

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“…The compressive failure of asperities is postponed. This finding is in line with Abass et al (2006) observations. The well that might be represented by the pair CP-13 and CP-14, CP-19 and CP-20 could be good candidate to acid fracturing once the conductivity curves passes within or near acid fracturing envelope.…”

Section: Conductivity Results -supporting

confidence: 95%

Building Acid Frac Conductivity in Highly-Confined Carbonates

et al. 2012

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The deep and hard limestones found off-shore Brazil are being extensively evaluated, and some of them would require stimulation to enable commercial development. The main objective of this paper is to discuss the feasibility of acid fracturing stimulation in hard carbonates. Laboratory test are performed to verify whether an acid-induced fracture can withstand the high effective normal stresses expected during the exploitation stage of pre-salt development, keeping an acceptable conductivity. There is no agreement in the technical community regarding the survival of an acid fracture at closure stress greater than 5,000 psi. However, the experience that leads to this controversy is mainly based on: (1) wells on land and, (2) few published tests on rocks with mechanical properties compatible with those depths. An experimental program has been designed to evaluate these chances of acid fracture survival. A few initial essays with samples of these carbonate rocks have shown significantly higher rock strength than those commonly found in the literature. Initially, the Nierode & Kruk correlation (1973) is used to predict fracture conductivity behavior. Both mechanical strength and dissolved rock equivalent conductivity are measured from outcrops, and from soft and hard offshore carbonates samples. This work reports the results with outcrops and reservoir samples, in order to assess whether the adopted experimental methodology is consistent and reproducible. Some topics about acid fracture conductivity prediction are also addressed. Further research should be performed with pre-salt rock samples using the same procedures. IntroductionOpen and conductive acid fractures are difficult to obtain. The existence of such fracture depends on the resistance of their asperities, ridges, hills and valleys to avoid being overwhelmed by the rock that surrounds it. Could the Argonauts feat be replicated and an acid fracture is maintained always open? According to myth, the passage of the Argonauts on Argó through the Symplegades, the clashing rocks, anchored and kept these rocks forever open in the Bosphorus strait. The analogy with an acid fracture is direct. Unfortunately maintain an acid fracture always open is also a myth. Sometimes, acid fractures close.

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Section: Conductivity Results -supporting

confidence: 95%

Building Acid Frac Conductivity in Highly-Confined Carbonates

et al. 2012

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“…To study the effect of acid on rock strength, we have systematically measured two parameters in each experiment in addition to the conductivity, the RES before and after acidizing, and the change in the vertical depth on the acidized surface by means of a 3D surface profile apparatus 5 . From these measurements we determined the coordinates of the high and low points of the etched core to compare with the coordinates of the RES measurements.…”

Section: Resultsmentioning

confidence: 99%

“…Even though formation hardness tests were not performed on the core samples, from their results, authors observed that more etched volume did not always result in higher conductivities. Abass et al 5 have performed experimental studies to investigate the effect of creeping on acid fracture conductivity. They recognized that acid weakens the contact points, causing a susceptible surface to creeping.…”

Section: Introductionmentioning

confidence: 99%

The Effects of Acid Contact Time and the Resulting Weakening of the Rock Surfaces on Acid-Fracture Conductivity

et al. 2007

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TX 75083-3836, U.S.A., fax 01-972-952-9435. initial Rock Embedment Strength (RES) values or a lager reduction in RES after acid injection have lower conductivity after closure. Measurements and analyses of rock embedment strength provide understanding of the conductivity behavior in acid fracturing.The results of preliminary tests for a North Sea chalk are also presented and discussed in the paper.

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“…Abass et al (2003) has demonstrated that in case of high in-situ stress, an etched fracture may significantly lose conductivity as a result of creeping effect.…”

Section: Acid Fracturingmentioning

confidence: 99%

Experience of Carbonate Acidizing in the Challenging Environment of the Volga-Urals Region of Russia

Kayumov

Konchenko

Bairamov

et al. 2014

SPE International Symposium and Exhibition on Formation Damage Control

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The Volga-Urals basin is one of the largest oil-producing regions in Russia. Orenburg region is essential part of Volga-Urals basin and it represents most of the challenges encountered in the other parts of the basin. More than half the wells produce exclusively from carbonate formations and require periodic acidizing treatments to maintain economic production. Carbonate stimulation treatments are usually based on pumping of hydrochloric acid into the formation with use of special diverters to maximize zone coverage by acid treatment. Some of the formation properties in Volga-Urals basin create additional challenges for successful acidizing treatments, including significant reservoir pressure depletion, high water cut, formation heterogeneity with high-and low-permeability strikes, low reservoir temperature, crude with tendency for emulsion and sludge creation, and enormous thief zones created by previous acidizing treatments. In many cases, uncertainties in the formation properties make the stimulation more complex.Carbonate stimulation practices in the Orenburg region have continuously improved during the last 6 years. First, degradable balls and polymer self-diverting acid were introduced to improve zone coverage. Later, viscoelastic self-diverting acid was added to eliminate damage associated with the polymer, and a viscoelastic selective diverter was used to minimize the probability of an increase in water cut after the treatment. Finally, foam was placed as a diversion agent, with and without coiled tubing (CT), to account for reservoir pressure depletion and help in post-acidizing flowback. Many lessons were learned, resulting in recommendations for use of various technologies at different reservoir and wellbore conditions.In addition to the recommendations for technologies, a quality assurance and quality control (QAQC) standard was developed and implemented for acidizing treatments. Moreover, laboratory work such as core flow testing and proppant embedment tests has been undertaken to clarify post-treatment aspects.Most fields in the Orenburg region are old, which implies that quality of well candidates became worse from year to year. However, with continuous improvement in stimulation practices and rigorous quality control we manage to maintain production at economic level and even increase work scope compared with previous years. This paper presents the experience gained during the 6-year of acidizing treatments in Orenburg region with lessons learned, and best practices adopted.

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Acid Fracturing or Proppant Fracturing in Carbonate Formation? A Rock Mechanics View

Cited by 23 publications

References 6 publications

Building Acid Frac Conductivity in Highly-Confined Carbonates

Building Acid Frac Conductivity in Highly-Confined Carbonates

The Effects of Acid Contact Time and the Resulting Weakening of the Rock Surfaces on Acid-Fracture Conductivity

Experience of Carbonate Acidizing in the Challenging Environment of the Volga-Urals Region of Russia

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