Wellbore Stability Model for Standalone Liner Completed Wells in Carbonate Reservoirs Subjected to Acidizing Jobs – II. Wellbore Stability Simulator

Santos, Erick Slis Raggio; Ferreira, Francisco H. G.

doi:10.4043/26280-ms

Cited by 4 publications

(4 citation statements)

References 17 publications

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“…The authors of this paper remember that the developed wellbore stability model continues in the companion paper OTC-26290-MS (Santos and Ferreira, 2015). This second paper describes how the rock softening evidences found here were used to build the standalone stability criteria.…”

Section: Final Remarksmentioning

confidence: 95%

“…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. 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.…”

Section: Forewordmentioning

confidence: 99%

“…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. These analyses should comprehend the effects of production drawdown and reservoir depletion state anticipated by the production plan.…”

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confidence: 99%

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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: Final Remarksmentioning

confidence: 95%

Section: Forewordmentioning

confidence: 99%

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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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“…The stability conditions depend on the establishment of sufficient hoop stresses capable of balancing the external load on the formation, otherwise, the rock particles may fail while drilling [31].…”

Section: Preventive Measures For Wellbore Stability Problemsmentioning

confidence: 99%

Wellbore Stability Problems in Deepwater Gas Wells

Aregbe¹

2017

WJET

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The analysis of wellbore stability in deepwater gas wells is vital for effective drilling operations, especially in deepwater remote areas and for modern drilling technologies. Wellbore stability problems usually occur when drilling through hydrocarbon formations such as shale, unconsolidated sandstone, fractured carbonate formations and HPHT formations with narrow safety mud window. These problems can significantly affect drilling time, costs and the whole drilling operations. In deepwater gas wells, there is also the possible of gas hydrate problems because of the low temperature and high pressure conditions of the environment as well as the coexistence of gas and water inside the wellbore. These hydrates can block the mud line, surface choke line and even the BOP stack if no hydrate preventive measures are considered. In addition, the dissociation of these hydrates in the wellbore may gasify the drilling fluid and reduce drilling mud density, hydrostatic pressure, change mud rheology and cause wellbore instabilities. Traditional wellbore stability analysis considered the formation to be isotropic and assumed that the rock mechanical properties are independent of in-situ stress direction. This assumption is invalid for formations with layers or natural fractures because the presence of these geological features will influence rock anisotropic properties, wellbore stress concentration and failure behavior. This is a complicated phenomenon because the stress distribution around a wellbore is affected by factors such as rock properties, far-field principal stresses, wellbore trajectory, formation pore pressure, reservoir and drilling fluids properties and time. This research work reviews the major causes of wellbore stability problems in deepwater gas wells and outlines different preventive measures for effective drilling operation, because real-time monitoring of drilling process can provide necessary information for solving any wellbore stability problems in a short time.

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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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Wellbore Stability Model for Standalone Liner Completed Wells in Carbonate Reservoirs Subjected to Acidizing Jobs – II. Wellbore Stability Simulator

Cited by 4 publications

References 17 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 Problems in Deepwater Gas Wells

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

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