Case Study of Multiple-Hydraulic-Fracture Completion in a Subsea Horizontal Well, Campos Basin

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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Acid or Propped Fracturing in Deep Carbonates? Experiments and Field Results

Oliveira

Neumann

Azevedo

2014

SPE International Symposium and Exhibition on Formation Damage Control

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The deep and hard carbonates found offshore Brazil are being extensively evaluated, and some of them would require fracture stimulation to enable commercial development. Due to the high effective normal stresses expected during the exploitation stage of pre-salt development, acid fractures could have very low conductivity values, depending on formation mechanical properties. Since perform propped fractures is more risky, it is important to create selection criteria to know precisely the fracture technique to be used. 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. This article aims to discuss Petrobras’ fracturing selection criteria development. The experimental data currently available for acid fracturing Brazilian deep carbonates will be presented. Laboratory test are performed to verify whether an acid induced fracture can withstand high effective normal stresses, keeping an acceptable conductivity. Key mechanical properties are measured in order to understand acid fracture conductivity behavior under stress. These mechanical properties are correlated with log data to allow the use of laboratory results on the fracture technique decision of a particular well. Field data regarding acid fractures wells will also be addressed.

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Case Study of Multiple-Hydraulic-Fracture Completion in a Subsea Horizontal Well, Campos Basin

Cited by 3 publications

References 14 publications

Improved understanding of proppant embedment behavior under reservoir conditions: A review study

Improved understanding of proppant embedment behavior under reservoir conditions: A review study

Building Acid Frac Conductivity in Highly-Confined Carbonates

Acid or Propped Fracturing in Deep Carbonates? Experiments and Field Results

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