Estimation of Horizontal-Well Productivity Loss Caused by Formation Damage on the Basis of Numerical Modeling and Laboratory-Testing Data

SPE Journal ◽  
2018 ◽  
Vol 24 (01) ◽  
pp. 44-59 ◽  
Author(s):  
Dmitry D. Vodorezov
Keyword(s):  
Analytical Solutions ◽  
Laboratory Testing ◽  
Horizontal Well ◽  
Damage Zone ◽  
Formation Damage ◽  
Well Productivity ◽  
Skin Factor ◽  
Damaged Zone ◽  
Variable Distribution ◽  
The Impact

Summary This paper presents a new numerical model of inflow to a well with a zone of damaged permeability. It is built on the principle of dividing the wellbore and damaged permeability zone into numerous segments. Simultaneous work of the segments is modeled with the method of velocity-potential theory. The model is applicable for wellbores of different trajectories including horizontal and multilateral wells. The model is focused on the extended application of results obtained during laboratory core testing that include a return-permeability (RP) profile of the core and cleanup parameters. The developed solution includes the effects of anisotropy, reservoir-boundary conditions, and a nonuniform distribution of formation damage in both radial and axial directions. The paper presents the new approach to include depth-variable distribution of damage in skin-factor models. The approach provides for the evaluation of pressure drop in a depth-variable damage zone by the resulting permeability that is defined by flow regime. Laboratory-obtained overall core permeability is associated with a linear flow, and when applied to a zone near the wellbore with radial or elliptic flow, it causes an error because of the depth-variable distribution of damage. The provided numerical simulations show that the impact of this factor on horizontal-well productivity is significant. The developed model is compared with existing analytical solutions of Furui et al. (2002) (FZH) and Frick and Economides (1993) (FE) for the case of a horizontal well with a cone-shaped damaged zone. The results show that a skin-factor transformation originally proposed by Renard and Dupuy (1991) for a case of a uniformly damaged well can be used successfully for the referred-to analytical solutions, which makes them applicable for wells with an elliptic drainage area. In this paper, we also suggest an approach whereby we relate the characteristics of the cleanup of the region near the wellbore to laboratory-testing conditions.

Evaporative Cleanup of Water Blocks in Gas Wells

SPE Journal ◽  
2007 ◽  
Vol 12 (02) ◽  
pp. 209-216 ◽  
Author(s):  
Jagannathan Mahadevan ◽  
Mukul Mani Sharma ◽  
Yannis C. Yortsos
Keyword(s):  
Capillary Pressure ◽  
Damage Zone ◽  
Low Permeability ◽  
Tight Gas ◽  
High Permeability ◽  
Water Displacement ◽  
Gas Wells ◽  
Well Productivity ◽  
Gas Expansion ◽  
The Impact

Summary The flow of a gas toward the wellbore of a production well will result in the evaporative cleanup of water blocks, if the latter exist. This occurs primarily due to gas expansion. This paper presents for the first time a model to calculate the rate at which such water blocks are removed, for either fractured or unfractured gas wells. The model allows us to compute the impact of evaporative cleaning on well productivity. The removal of water first occurs by gas displacement. Evaporative cleanup is caused by gas expansion. The resulting saturation profile is qualitatively different for low- or high-permeability rocks. As a consequence, the increase in gas relative permeability, or the well productivity, with time can vary depending on the rock permeability and the well drawdown. High-permeability (e.g. fractured) rocks clean up significantly faster. By contrast, low-permeability unfractured wells may require a very long time to clean up. Large pressure drawdowns, as well as the use of more volatile fluids, such as alcohols, also result in faster cleanup. A distinctive feature of the work presented is that the model equations are formulated and solved completely without the assumption of skin factors for the damage zone. Thus, the prediction of cleanup rates can be made more accurately. Introduction Water blocks in low-permeability rocks clean up much more slowly than those of higher permeability because of the smaller pore sizes and the consequent higher capillary entry pressures (Mahadevan et al. 2003). In particular, water blocks in tight gas sands are not easily cleaned up, especially in cases where the reservoir pressures are too low to initiate flow. Past studies (Tannich 1975; Holditch 1979, Parekh and Sharma 2004) have reported the effect of water displacement by gas in the cleanup of water blocks in gas wells. They showed that when the drawdown in the gas well is significantly larger than the capillary pressure, cleanup is faster. However, in cases where the drawdown becomes comparable to the capillary pressure, as is the case in depleted tight gas reservoirs, displacement alone is not sufficient to remove water from the near-wellbore region. Subsequent water removal occurs by evaporation. The flow of a fully saturated compressible gas through a water-saturated porous rock induces evaporation. Roughly, this is because the volume of the gas, and hence its capacity for water content, increases as pressure declines. In past studies, the impact of evaporation caused by the flow of gas has been neglected. The focus of this paper is precisely on this regime in gas wells, in which the drawdown is comparable in magnitude to the capillary entry pressure, and cleanup of water blocks is by evaporation.

Excavation Damage Zone in the Experimental Deposition Holes at Äspö and Comparison to Existing Data

2003 ◽  
Vol 807 ◽  
Author(s):  
Jorma Autio ◽  
Hanna Malmlund ◽  
Thomas Hjerpe ◽  
Maarit Kelokaski ◽  
Marja Siitari-Kauppi
Keyword(s):  
Hard Rock ◽  
Damage Zone ◽  
High Level Waste ◽  
Excavation Damaged Zone ◽  
Damaged Zone ◽  
Crushed Zone ◽  
High Level ◽  
Excavation Damage ◽  
The Impact ◽  
Clear Increase

ABSTRACTDisposal in deep, stable bedrock is currently one concept for isolating high-level wastes from the environment. Repository for high-level waste in rock excavated using different drilling techniques is surrounded by an excavation damaged zone (EDZ) which properties have been changed. The micro fracturing of samples taken from the experimental deposition holes in the underground Hard Rock Laboratory at Äspö were investigated by the 14C polymethylmetha-crylate (14C-PMMA) method and scanning electron microscopy (SEM) to evaluate the impact of EDZ on migration. The porosity of the damaged rock zone is clearly higher than the porosity of undisturbed rock. The thickness of the crushed zone with significantly higher porosity is a few millimetres and the average depth of the damaged zone (i.e. a clear increase in porosity found) is from 5 to 20 mm from the hole wall. The apertures of the inter- and intragranular fractures in the crushed zone varied from 5 to 30 μm according to SEM examination. Earlier results of porosity, diffusivity and permeability measurements in granites were compiled and the results of the porosity values of Äspö diorite were compared to the porosity values measured in other types of granites. The results were compiled in permeability-diffusivity-porosity space and were found to form a plane that could be used to estimate the range of diffusivity and permeability of the Äspö diorite.

scholarly journals Study on Skin Factor and Productivity of Horizontal Well after Acidizing with Nonuniform Damage

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Lin Yuan ◽  
Xiao-Ping Li ◽  
Xiao-Hua Tan ◽  
Lie-Hui Zhang
Keyword(s):  
Horizontal Well ◽  
Present Model ◽  
Damage Zone ◽  
Local Skin ◽  
Type Curves ◽  
Filtration Resistance ◽  
Skin Factor

Horizontal well (HW) was divided into several elements after acidizing. In each element, there would exist a composite zone that was made up of damage zone (DZ) and acidizing zone (AZ). Local skin factor after acidizing was used to describe the resistance in each composite zone. The models for local skin factor and productivity of HW were created using the method of equivalent filtration resistance and displacement between two similar flow modes. According to the solution of the models, type curves of skin factor and production-increasing ratio after acidizing were illustrated, and the effect of different parameters in DZ and AZ on distribution of skin factor and production-increasing ratio after acidizing were discussed. The present model has a significant guide on the practice of acidizing technology.

scholarly journals Modified Horizontal Well Productivity Model for a Tight Gas Reservoir Subjected to Non-Uniform Damage and Turbulence

Energies ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 8334
Author(s):  
Samuel O. Osisanya ◽  
Ajayi Temitope Ayokunle ◽  
Bisweswar Ghosh ◽  
Abhijith Suboyin
Keyword(s):  
Flow Rate ◽  
Horizontal Well ◽  
Horizontal Wells ◽  
Total Production ◽  
Tight Gas ◽  
Gas Reservoirs ◽  
Well Productivity ◽  
Tight Gas Reservoirs ◽  
Skin Factor ◽  
Tight Gas Reservoir

Tight gas reservoirs are finding greater interest with the advancement of technology and realistic prediction of flow rate and pressure from such wells are critical in project economics. This paper presents a modified productivity equation for tight gas horizontal wells by modifying the mechanical skin factor to account for non-uniform formation damage along with the incorporation of turbulence effect in the near-wellbore region. Hawkin’s formula for calculating skin factor considers the radius of damage as a constant value, which is less accurate in low-permeability tight gas reservoirs. This paper uses a multi-segment horizontal well approach to develop the local skin factors and the equivalent skin factor by equating the total production from the entire horizontal well to the sum of the flow from individual segmented damaged zones along the well length. Conical and horn-shaped damaged profiles are used to develop the equivalent skin used in the horizontal well productivity equation. The productivity model is applied to a case study involving the development of a tight gas field with horizontal wells. The influence of the horizontal well length, damaged zone permeability, drainage area, reservoir thickness, and wellbore diameter on the calculated equivalent skin (of a non-uniform skin distribution) and the flow rate (with turbulence and no turbulence) are investigated. The results obtained from this investigation show significant potential to assist in making practical decisions on the favorable parameters for the success of the field development in terms of equivalent skin factor, flow rate, and inflow performance relationships (IPR).

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