Openhole Stability Analysis of Horizontal Wellbores Under Production Scenarios in Jurassic Carbonate Reservoirs of West Kuwait

Franquet, Javier; Verma, Naveen; Azeemuddin, Mohammed; Shamali, Adnan Aiesh Al; Al-Morakhi, Rasha; Reji, E.C.

doi:10.2118/105332-ms

Cited by 4 publications

(1 citation statement)

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“…Only a few authors have shown concerns that acid treatments could reduce the mechanical properties of carbonates so that early wellbore failure could take place (Morita et al, 2002;Montgomery et al, 2005;Franquet et al, 2007;Nguyen et al, 2011;Bauer et al, 2013). Only a few authors have shown concerns that acid treatments could reduce the mechanical properties of carbonates so that early wellbore failure could take place (Morita et al, 2002;Montgomery et al, 2005;Franquet et al, 2007;Nguyen et al, 2011;Bauer et al, 2013).…”

Section: Discussionmentioning

confidence: 99%

Wellbore Stability Model for Standalone Liner Completed Wells in Carbonate Reservoirs Subjected to Acidizing Jobs - I. Dissolution-Induced Mechanical Weakening Model

Santos

Ferreira

2015

Day 1 Tue, October 27, 2015

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Mechanical stability analyses are mandatory to identify suitable candidates for openhole completions. These analyses should comprehend the effects of production drawdown and reservoir depletion state anticipated by the production plan. The understanding and modeling of the physico-chemical interactions between rock and flown fluids and their impacts on the rock mechanical properties is imperative in the openhole stability analysis of wellbores drilled in carbonate reservoir rocks, especially in the wells subjected to acid stimulation. This paper presents a methodology for determining the impact of stimulation jobs in the confined rock mechanical response and thus on the acidized wellbore stability. The authors briefly discuss the main rock dissolution patterns, ranging from compact dissolution to homogeneous, passing through the wormhole generation. The homogeneous dissolution pattern has been pursuit in the laboratory because of: i) absence of confident methods to anticipate which other pattern should be more dominant in a given scenario; and ii) Its highest impact on the mechanical properties, leading to safe analyses.As a result, 24 samples from an off-shore carbonate reservoir have been mechanically tested. 13 of these have been tested after a massive dissolution. The initial effective pore volume and its evolution due to dissolution have been registered and were applied as a geomechanics indicator. The triaxial test results show that the rock softens during injection with impacts on its kinematic parameters. The ultimate rock strength, otherwise, remained almost unchanged. An analytical expression has been devised to map the porosity variations in the wellbore surroundings based on the acid job operational parameters. It indicates that the main failure behavior of a uncased wellbore subjected to acidizing jobs or non-native fluid flows should be related to excessive near wellbore rock straining rather than brittle failures. In this scenario, a standalone completion scheme would be preferable against the barefoot because of its ability to provide mechanical support to the altered rock at the borehole walls.The current dissolution-induced rock weakening model presents a significant increase in the understanding on how the acid job affects the carbonate rock mechanical response, building a solid base for the well integrity analyses in the production phase. ForewordThis is the first of two companion papers, namely the OTC-26290-MS and OTC-26290-MS, intended to present the new methodology Petrobras has developed to evaluate the mechanical stability of standalone completed wells for a large offshore carbonate reservoir in Brazil subjected to acid stimulation. The second paper (Santos and Ferreira, 2015) describes the devised standalone liner completed wellbore stability model, considering the dissolution-induced rock weakening model here described.

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Section: Discussionmentioning

confidence: 99%

Wellbore Stability Model for Standalone Liner Completed Wells in Carbonate Reservoirs Subjected to Acidizing Jobs - I. Dissolution-Induced Mechanical Weakening Model

Santos

Ferreira

2015

Day 1 Tue, October 27, 2015

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Wellbore Stability: A Critical Review and Introduction to DEM

Kang

Miska

et al. 2009

All Days

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Borehole stability issues are always a spotlight in drilling activities because of their costly consequences, including borehole collapse, lost circulation, stuck pipe etc. Wellbore instability is primarily a function of how rocks respond to the induced stress concentration around the wellbore during various drilling activities. By considering different failure mechanisms between the formation and drilling fluid interaction, several major wellbore models have been presented over the last seventy years. Those models take into account the mechanical, chemical, hydraulic, or thermal effects between the drilling fluid and the formation, or couple two or more effects in a model. The time effect is also taken into account in some of the models. In most of the models,the rock is treated as a continuous materialborehole failure is normally based on single initial failure point. However, rocks are discontinuous materials formed under an environment of complex stresses. Also, it is likely an overstatement to say that instability occurs when only one point fails. Even if a small group of grains disconnects from wellbore, the well can still be stable. While somewhat irregular (noncircular) the wellbore can still accommodate casing and installation of down-hole equipment. Therefore, this paper also introduces a new approach based on grain-scale discrete element modeling (DEM) to mimic the realistic rock condition. The rock is modeled as an assembly of numerous grains bonded by cement-like materials, and pore spaces are formed between the small grains. The dynamics of rock grains is simulated and tracked on a computer. Micro cracks (because of tensile or shear failure) occurring at stress-concentrated zones and their coalescence to form macro fractures are tracked. The borehole shape and size are tracked with time. This paper is useful to those who wish to understand the main limitations of the conventional models and the potential usefulness of a new approach based on a discrete element method (DEM). The approach presented in this paper can also help engineers understand how wellbore instability (post-initial failure) develops with time. Introduction Subsurface rocks are under a balanced stress condition before a well is drilled. Such equilibrium will be disturbed when a well is drilled. Although drilling fluid can partially support the wellbore surface, the presence of a wellbore can cause the redistribution of stresses around the borehole. If the stress concentration exceeds the strength of the rock, failure in the nearwellbore region occurs. Wellbore stability is a major concern in drilling operations. It is the major cause of nonproductive time during drilling operation and costs the oil and gas industry more than $6 billion USD worldwide annually (SPE review, SPE-UK, 2005). With the increasing demand of energy (oil and gas), drilling operations move to the direction where more and more harsh environments are encountered. With more wells to be drilled under high pressure and high temperature conditions, the industry expects more severe wellbore stability problems to occur. Although wellbore stability has been studied (experimentally and theoretically) for many years, it remains one of the major challenges for the oil and gas industry due to the complex nature of the drilled formations. Therefore a better understanding of wellbore stability is of imperative importance for the oil and gas industry. In this paper, the discrete element method (DEM) is adopted in this study to get a better understanding of time-dependent transient wellbore instability that takes place in a realistic rock condition.

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Improved Recovery of Carbonate Reservoir by Optimizing Acidizing Strategy; Coupled Wellbore, Reservoir, and Geomechanical Analysis

Safari

Smith

Fragachán

2017

Day 3 Wed, November 15, 2017

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One of the sources of damage in stimulated carbonate rock is the loss of near wellbore formation compressive strength which may results in casing collapse under extreme conditions. Field studies have shown that the failure of acidized rock may cause damage and thereby negatively impact production. In this work, an integrated analysis workflow is presented to simulate acid placement in carbonate reservoirs and model stimulated rock behavior during the productive lifetime of the well. The workflow is utilized to design a unique approach to horizontal wellbore acidizing and optimize the strategy to maximize hydrocarbon recovery. The presented workflow is based on the interaction between the distributions of reactive fluid along a wellbore, a two scale continuum model to simulate porosity evolution during stimulation, and stimulated rock performance during production time. The model first simulates stimulation fluid movement in the wellbore and couples it with transient reservoir flow. The primary analysis provides the distribution of reactive fluid along the well. The rock dissolution at each section of reservoir is then analyzed by continuum two-scale model (pore-scale and Darcy scale). This analysis presents porosity evolution at different locations along the well and at different radial distance from the wellbore center. Then, the developed geomechanical engine simulates the weakened rock under the in-situ stresses and bottom-hole pressure and predicts any possible compressional or shear failure. The effect of rock failure is then considered on the production prediction. The workflow is best used to analyze and optimize acid stimulation for a horizontal well. The analysis results show that the induced wormholes are stable and open since reservoir depletion increases the effective mean stress. At the elevated mean effective stress, wormholes or pores start to collapse and the failure extended away from near wellbore region and neutralized the stimulation effects. Since in the acid treated zone the rock is softened, the stress concentration around the wellbore might extended more into the reservoir. Analyzing this phenomenon showed that at a certain level of lowered stress concentration extension, in other words at certain strength and volume of acid, the wormhole can be stable and open during expected production time. Furthermore, the coupled analysis also demonstrates that at specific environment, the wormholes penetrated further into the rock, longer than possible induced failure. The workflow can be used to determine how weak or strong the acid should be at specific environmental condition to have longer life for the induced wormholes and hence extra hydrocarbon recovery.

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Openhole Stability Analysis of Horizontal Wellbores Under Production Scenarios in Jurassic Carbonate Reservoirs of West Kuwait

Cited by 4 publications

References 10 publications

Wellbore Stability Model for Standalone Liner Completed Wells in Carbonate Reservoirs Subjected to Acidizing Jobs - I. Dissolution-Induced Mechanical Weakening Model

Wellbore Stability Model for Standalone Liner Completed Wells in Carbonate Reservoirs Subjected to Acidizing Jobs - I. Dissolution-Induced Mechanical Weakening Model

Wellbore Stability: A Critical Review and Introduction to DEM

Improved Recovery of Carbonate Reservoir by Optimizing Acidizing Strategy; Coupled Wellbore, Reservoir, and Geomechanical Analysis

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