The pressure exerted on the formation by the drilling fluids bottom hole pressure is greater than the opposing pressure of the formation fluids pore pressure. Overbalance pressure an overview sciencedirect topics. This results in the majority of underbalanced horizontal wells being overbalanced for some fraction of the time during the drilling and completion process. A growing recognition of the importance of drilling induced formation damage has led to the use of drillin fluids fluids used to drill through the pay zone that minimize formation damage.
This page discusses the formation damage that may be associated with various types of drilling fluids. Underbalanced drilling and completion operations are not necessarily a panacea for all formation damage problems and. Pdf formation damage and reservoir considerations for. Ubd is implemented predominantly to maximize the production capacity variable of the wells optimization by minimizing formation damage during the drilling process. Underbalanced drilling and formation damage is it a. Formation damage in underbalanced drilling operations core. Underbalanced drilling is not a solution for all formationdamage problems.
Underbalanced drilling an overview sciencedirect topics. A simple analytical approach to simulate underbalanced. A summary of this work is provided in the iiterature16. Experimental study of formation damage during underbalanced. Loss circulation and formation damage control on overbalanced drilling with different formulations of water based drillin fluids on sandstone reservoir. Underbalanced drilling ubd has been used with increasing frequency to minimize problems associated with invasive formation damage, which often greatly reduce the productivity of oil and gas reservoirs, particularly in openhole horizontal well applications.
Formation damage dd formation pressure and hydrocarbon depletion d x. Experiments of drilling and completion fluid damage evaluation. How to predict formation pressure prior to drilling. Introduction to underbalanced and overbalanced drilling operations hd like our facebook.
It also presents advantages and disadvantages that each method presents. During overbalanced drilling obd, mud and mud filtrate penetrate the nearwellbore formation because of this overbalanced pressure, altering nearwell flow properties. Pdf a comparison of underbalanced and overbalanced drilling. Overbalanced drilling is always regarded as the conventional way of drilling a well. However, indepth understanding of the characteristic behavior of different components during operation is an essential criteria for efficient application of this technology.
In workover and wellservicing situations, well control commands special considerations editors note. One approach to minimize formation damage is to use drillin or completion fluids that are specially formulated to avoid damage to the formation when drilling pay zones, rather than ordinary drilling. Underbalanced drilling is not a solution for all formation damage problems. This excess pressure is needed to prevent reservoir fluids oil, gas, water from entering the wellbore. Other formations or fields may not be viable for a variety of reasons. Comparative study between overbalanced and underbalanced oil drilling methods abstract the technique used worldwide while drilling is known as overbalanced drilling. To mitigate formation damage due to the waterinoil drilling mud, it has been. Third, chemical reactions between the drilling fluid and the formation rock and fluids can precipitate solids or semisolids that plug pore spaces.
Which is defined as the drilling process where the hydrostatic pressure used exceeds the formation pressure. While it is widely accepted that underbalanced drilling greatly reduces the propensity for. Mechanisms of formation damage and permeability impairment associated with the drilling, completion and production of low api gravity oil reservoirs d. A comparison of underbalanced and overbalanced drilling induced formation damage using reservoir conditions core flood testing. If the completion fluid is incompatible with the reservoir, the invasion of solids and liquid phase must cause formation damage. Prepared for presentation at the 6th international conference on. Underbalanced drilling and formation damage is it a total.
This paper discusses major points that drilling operations consider before making choice between underbalanced and overbalanced drilling methods. Overbalanced drilling, or obd, is a procedure used to drill oil and gas wells where the. Formation damage in underbalanced drilling operations. Preventing invasive drilling mud solids and fluids from causing near wellbore formation skin damage increases production rates and can remove the need for costly completion and stimulation operations. Abstract reservoir conditions core flood tests have been carried out to examine the damage arising from overbalanced drilling in operations. Dynamic damage evaluation instrumentation system of drilling and completion fluid. Spe 60325 formation damage processes reducing prodlk. Formation damage is often caused by invasion of normal drilling fluids that contain barite or bentonite. Various authors1 have documented why concerns with formation damage in.
Underbalanced drilling of horizontal wells hycal energy research. Conventional drilling utilizes a singlephase drilling fluid, which works on the premise of keeping an overbalanced pressure at. Whether the underbalanced status is induced or natural, the result may be an influx of formation fluids that must be circulated from the well, and controlled at surface. A simple analytical approach to simulate underbalanced drilling in naturally fractured reservoirsthe effect of short overbalanced conditions and time effect siroos salimi 1, ali ghalambor 2, johan tronvoll 3 and knut inge andersen 4 1 norwegian university of science and technology ntnun7491, trondheim, norway. Underbalanced drilling, formation damage, rate of penetration loss of circulation and down hole challenges. Bietz hycal energy research laboratories ltd abstract 9, formation damage issues peculiar to the drilling and. Tubing directional drilling system the ctdirect coiled tubing directional drilling system minimizes reservoir damage during underbalanced or. Introduction to underbalanced and overbalanced drilling operations hd. Can lead to severe damage to bit and drillstring different designs to. It is well known that formation damage caused by drilling fluid has a huge impact on a wells oil and gas productivity, especially for openhole completed horizontal wells. A relatively new technique was introduced, known as underbalanced drilling, where the well is being drilled with a hydrostatic pressure less than that of the formation. A comparison of underbalanced and overbalanced drillinginduced formation damage using reservoir conditions core flood testing. Pdf a comparison of underbalanced and overbalanced. Such problems are differential pipe sticking, loss of circulation, formation damage and other problems.
Perhaps the most important benefit of such drilling is the reduction of damage to the natural oil and gas formation. Experimental results indicate that the drilling fluid causes the major damage, and. This is especially true in overbalanced perforating where the fluid being used is not compatible. The objective is to reduce formation damage and the related fluid losses when drilling deep formations with lowfracture gradients eliminating mud density changes reference 1. Formation damage during underbalanced drilling is created due to the spontaneous countercurrent imbibition when drilling mud is in contact with saturated formations. The amount of pressure or force per unit area in the wellbore that exceeds the pressure of fluids in the formation. Introduction to underbalanced and overbalanced drilling. Proceedings of the asme 2012 31st international conference on ocean, offshore and arctic engineering. Experiments were conducted to investigate the influence of overbalance pressure on formation damage during drilling operations. Gannet field cores were exposed to a number of water and oilbased field muds currently in use by shell exp. This paper describes an experimental investigation of formation damage in a fractured carbonate core sample under underbalanced drilling ubd conditions. This is done with the main purpose of killing the well. However, excessive overbalance can dramatically slow the drilling process by effectively strengthening the nearwellbore rock and limiting removal of drilled cuttings.
Underbalanced drilling, or ubd, is a procedure used to drill oil and gas wells where the pressure in the wellbore is kept lower than the static pressure than the formation being drilled. Formation damage due to drilling and fracturing fluids and its. Performed with a lightweight drilling mud that applies less pressure than formation pressure, underbalanced drilling prevents formation damage that can occur during conventional, or. Nearwellbore formation damage effects on well performance. Drilling bits depending on the formation type, hardness and abbrasiveness a proper bit has to be selected to optimise. As the well is being drilled, formation fluid flows into the wellbore and up to the surface. Recently, underbalanced drilling has been utilized as a.
When drillingin reservoir under overbalance pressure conditions, the drilling and completion fluid will be sure to enter the reservoir. Underbalanced drilling, or ubd, is a procedure used to drill oil and gas wells where the pressure in the wellbore is kept lower than the fluid pressure in. Comparative study between overbalanced and underbalanced. There are those situations where it is less expensive to accept some formation damage while drilling a well and using an inexpensive acid treatment to remove the damage after the well is cased and perforated. Permeability reduction due to formation damage by drilling fluids. However, excessive overbalance can dramatically slow the drilling process by effectively strengthening the nearwellbore rock and limiting removal of drilled cuttings under. A drilling operation is a udt if it does not follow the conventional drilling method as done in the majority of cases. In many other drilling techniques, the mud used for drilling and maintaining well pressure can be forced out of the well and into the reservoir deposit, possibly damaging the well and the operation overall. A discussion of mechanical damage due to near surface glazing effects is also presented as a possible mechanism of damage which can occur during underbalanced drilling. It can also be caused due to plugging by the solid contents in the mud. Mechanisms of formation damage and permeability impairment. Since hydrostatic head of drilling fluid is less in ubd, there is no chances of invasion by drilling fluids into. Payzone damage, including fine solids migration, clay swelling and solids invasion, reduces effective formation permeability, which results in lower production rates. Effect of overbalance pressure on formation damage request pdf.
Abstract underbalanced drilling has been utilized as a technique to minimize damage due to whole mud, fluid filtrate and solids invasion into high. Pdf mathematical modeling of formation damage effect. This damage is mainly caused by washout or physical blockage by the intrusion of fluids andor solids into the formation structure. Formation damage processes reducing productivity of low permeability gas reservoirs d. Introduction formation damage occurring during the drilling of horizontal or vertical wells can be a significant mechanism. Underbalanced drilling ubd technology can overcome a number of problems encountered during drilling, which is otherwise impossible with conventional overbalanced drilling. In underbalanced drilling ubd, the hydrostatic head of the drilling fluid is intentionally designed to be lower than the pressure of the formations that are being drilled. In overbalanced drilling, the bottom hole wellbore pressure is kept higher than the formation fluid pressure during drilling operation.
The technique used worldwide while drilling is known as overbalanced drilling. If formation damage is the main driver for ubd, it is important that the reservoir and petroleum engineers understand the damage mechanisms resulting from overbalanced drilling obd. Introduction the current drilling practice in the olkaria geothermal field is a mixture of both overbalanced drilling, near balance drilling and balanced drilling. The petroleum drilling industry drills many well sections using some type of unconventional drilling technique udt. The experimental procedure consists of 1 forward measuring formation water. A geothermal well comprises of surface hole, intermediate hole. Underbalanced drilling ubd is defined as the practice of drilling a well with the wellbore fluid.
This article discusses waterbase drillin fluid systems and applications. Formation damage and reservoir considerations for overbalanced and underbalanced ct operations d. Contribution of underbalanced drilling to production. A major portion of this study has concentrated on problems which are often associated with ubd and the development of a detailed protocol for proper design and execution of an ubd program. Operationally, the pressure of the borehole fluid column is reduced to less than the pressure in the zoi. However, there are numerous problems that accompany overbalanced drilling. Damage caused by poorly designed andor executed underbalanced drilling programs can equal or exceed that which may occur with a welldesigned conventional overbalanced drilling program. Experimental study of formation damage during underbalanceddrilling in naturally fractured formations, energies, vol.
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