Near-Wellbore Formation Damage Effects On Well Performance--A Comparison Between Underbalanced and Overbalanced Drilling
- Yu Ding (Institut Francais du Petrole IFP) | Benjamin Herzhaft (Institut Francais du Petrole IFP) | Gerard Renard (Institut Francais du Petrole IFP)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- February 2006
- Document Type
- Journal Paper
- 51 - 57
- 2006. Society of Petroleum Engineers
- 1.8.5 Phase Trapping, 1.8 Formation Damage, 5.6.8 Well Performance Monitoring, Inflow Performance, 5.2 Reservoir Fluid Dynamics, 4.3.1 Hydrates, 1.11 Drilling Fluids and Materials, 2.2.2 Perforating, 1.6 Drilling Operations, 5.5 Reservoir Simulation, 1.7.1 Underbalanced Drilling
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Prediction of formation damage that occurs while drilling horizontal wells is a critical point for optimizing an oil field's development. The economic impact of near-wellbore drilling-induced damage and cleanup efficiency has led to significant progress being made in both experimental and numerical studies in order to assess wellbore flow properties during oil production. As a result, a numerical model has been developed to study the impact of various parameters related to the properties of drilling fluids on well inflow performance.
This paper describes a numerical approach developed in this model to simulate near-wellbore formation damage caused by underbalanced drilling (UBD). It is generally expected that UBD will be of benefit by preventing formation damage. However, this benefit can be lost for various reasons. For instance, an overbalanced pressure can be applied on the formation during short periods of time for various operational reasons and can cause severe formation damage because of the absence of external cake protection and huge filtrate invasion. Another possible cause of formation damage in UBD is related to spontaneous imbibition, which induces waterblocking, which was observed while drilling tight gas reservoirs.
A methodology for the modeling of possible formation damage during UBD is presented. Crossflow phenomena caused by spontaneous imbibition is taken into account to model the filtrate invasion from the well to the porous media, as the well is in production.
It is well known that formation damage caused by drilling fluid has a huge impact on a well's oil and gas productivity, especially for openhole completed horizontal wells. During overbalanced drilling (OBD), mud and mud filtrate penetrate the near-wellbore formation because of this overbalanced pressure, altering near-well flow properties. As a result, well productivity is dramatically reduced. It is generally recognized that UBD can be used to minimize problems associated with invasive formation damage. When correctly performed, UBD reduces or eliminates invasive formation damage, improves access to reserves, and provides potential for reservoir evaluation while drilling. Additional benefits of UBD are the reduction in drilling time, high rates of penetration, and increase of bit life.
UBD has recently proven its efficiency in numerous situations in which serious problems were encountered with classical drilling techniques. For example, heavy loss formations or depleted zones are ideal candidates for UBD. During normal UBD, the negative pressure drop between the wellbore and the formation prevents drilling fluids from entering the formation. However, this benefit can be lost in at least two situations owing to possible sources of failure such as temporary overbalanced conditions or spontaneous imbibition. When drilling underbalanced, the fluid system is not designed to contain cake-building solids as in the case of overbalanced drilling. Thus, if underbalanced conditions cannot be maintained 100% of the time, severe losses can occur, which may result in formation damage. Overbalanced conditions may result from bit trips, running in, or other situations in which wellbore intervention is necessary. Spontaneous imbibition is particularly important in tight gas reservoirs.
Even though UBD has many advantages over OBD, it is necessary to quantify production improvement and possible formation damage, which is an important factor in evaluating the economic feasibility of UBD projects (Bennion and Thomas 1994; Bennion et al. 1994; Bennion et al. 1998; Cade et al. 2003; Suryanarayana et al. 2003; Xiong and Shan 2003).
This paper presents a numerical model allowing us to calculate well productivity reduction owing to possible formation damage during UBD, such as temporary overbalanced drilling or spontaneous imbibition.
The modeling of well performance in OBD has already been presented (Ding et al. 2002; Ding and Renard 2003). Both internal and external cakes are considered in the model, and filtrate invasion is calculated using a two-phase flow equation. Polymer absorption/retention, phase trapping, and wettability alteration are globally represented using a hysteresis of relative permeabilities. Nonuniform formation damage along the well is represented by variable specific skin factors through an optimization procedure. The change of well performance can therefore be calculated using a flow simulator by taking into account these variable skin factors.
In this paper, a methodology for the modeling of possible formation damage during UBD is presented. Formation damage related to temporary overbalanced pressure is considered. Spontaneous imbibition is modeled using two-phase flow simulation with capillary pressure. When capillary forces are important, countercurrent imbibition occurs with the flow of reservoir fluids toward the well while the filtrate invades the formation. Spontaneous imbibition is particularly important in tight gas reservoirs. Like the modeling of OBD, a hysteresis of relative permeabilities is used to represent globally various physics during drilling and backflow.
The impacts of formation damage on well productivity are simulated by the numerical model and are compared for both underbalanced and overbalanced drilling. The sensitivity to various parameters related to drilling conditions (underbalanced or overbalanced) and reservoir parameters is presented. Simulations show that formation damage in UBD depends on reservoir and applied drilling conditions. Damage is sometimes severe because of no filter cake protection. Therefore, operational precautions should be taken during UBD to prevent such damage. The proposed numerical model can be used as a selection guide between OBD and UBD for both well performance predictions and calculation of the best economic benefits on long-term production, assuming that some damage can be done to the near-wellbore formation while drilling underbalanced.
|File Size||1 MB||Number of Pages||7|
Bennion, D.B. and Thomas, F.B.: "Underbalanced Drilling of HorizontalWells: Does it Really Eliminate Formation Damage?" paper SPE 27352presented at the 1994 SPE Formation Damage Control Symposium, Lafayette,Lousiana, 7-10 February.
Bennion, D.B. et al.: "Underbalanced Drilling and Formation Damage—Is It aTotal Solution?" paper presented at the 1994 Annual Meeting of the PetroleumSociety of CIM, Calgary, 12-15 June.
Bennion, D.B. et al.: "Underbalanced Drilling: Praises andPerils," SPEDC (1998) 13, No. 4, 214.
Cade, R. et al.: "DoesUnderbalanced Drilling Really Add Reserves?" paper SPE 81626 presented atthe 2003 IADC/SPE Underbalanced Technology Conference and Exhibition, Houston,25-26 March.
Ding, Y. et al.: "Modeling ofBoth Near-Wellbore Damage and Natural Cleanup of Horizontal Wells Drilled Witha Water-Based Mud," paper SPE 73733 presented at the 2002 SPE InternationalSymposium and Exhibition on Formation Damage Control, Lafayette, Louisiana,20-21 February.
Ding, Y. and Renard, G. : "Modelling of Near-Wellbore FormationDamage for Openhole Horizontal Wells in Anisotropic Media," paper SPE 82255presented at the 2003 SPE European Formation Damage Conference, The Hague,13-14 May.
Suryanarayana, P.V. et al.: "Development of a Probabilistic ModelTo Estimate Productivity Improvement due to Underbalanced Drilling," paperSPE 81639 presented at the 2003 IADC/SPE Underbalanced Technology Conferenceand Exhibition, Houston, 25-26 March.
Xiong, H. and Shan, D.: "Reservoir Criteria for SelectingUnderbalanced Drilling Candidates," paper SPE 81621 presented at the 2003IADC/SPE Underbalanced Technology Conference and Exhibition, Houston, 25-26March.