Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH DRILLING; MINING
  • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B7/00—Special methods or apparatus for drilling
  • E21B7/18—Drilling by liquid or gas jets, with or without entrained pellets
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH DRILLING; MINING
  • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
  • E21B49/003—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells by analysing drilling variables or conditions

Definitions

• the invention is related to determining a property of a formation material in the course of a jet drilling operation, in particular into a subsurface earth
• properties of a formation material can be derived by analyzing cuttings which result from a conventional mechanical drilling action. Furthermore, it is known to apply downhole evaluation measurements like gamma-ray and neutron density logs. Properties like permeability and porosity can be derived from such measurements. As much as these properties can be of general interest to the geologist, for the process of mechanical drilling itself they are normally not considered important parameters as such.
• a fluid jet drill head which directs a fluid jet with erosive power into impingement with the borehole wall.
• a fluid mixture including a quantity of abrasive particles is employed.
• Such jet drilling is particularly well suited for making boreholes with a small diameter.
• a jet drill system and method of making a hole in an object is for example disclosed in WO-A-2005/005767.
• the known system comprises an excavating tool, herein also referred to as abrasive jet drill head, mounted on a lower end of a drill string that is inserted from the surface into a hole in a subterranean earth formation.
• the drill string is provided with a longitudinal passage for transporting a drilling fluid mixture comprising abrasive particles to the drill head.
• the drill head comprises jet means arranged to generate an abrasive jet in a jetting direction into impingement with the earth formation in an impingement area.
• the abrasive jet contains magnetic abrasive particles (steel shot) .
• a recirculation system which captures abrasive particles from the return stream to surface, after erosive impingement, by means of a magnet, and re-mixes the abrasive particles at a mixing location with the mixture received via the drill string.
• the magnet is arranged as a rotatable conveyor, attracting particles to be recycled and conveying them towards a mixing location with fresh fluid from surface.
• directional drilling is achieved by a modulation means in form of a controllable drive means for the conveyor, which is arranged so as to modulate the recirculation rate, and in this way the quantity of particles in the abrasive jet at the jet means is modulated.
• Jet drilling with or without abrasive particles, differs in many ways from mechanical drilling.
• a major difference is that jet drilling results in rock cuttings which are typically much smaller than the cuttings which result from mechanical drilling such as using rollercone or PDC drilling bits with cutters.
• the cuttings are predominantly fines which can hardly be distinguished with the bare eye, and larger chips are scarce.
• WO 2009/099945 discloses a particle impact drilling system and method. It is disclosed that the impactors may be selected based upon physical factors, for example one or more rock properties of the formation being excavated. It is also disclosed that a rate of penetration can be optimized by determining an excavation parameter, and by adjusting one or more controllable variables accordingly.
• Excavation parameters are parameters relating to the excavation method used.
• US 2006/0016622 discloses a method and system for excavating a subterranean formation using a high-velocity fluid with solid material impactors, wherein also
• excavation parameters are monitored, and at least one excavation parameter is altered accordingly.
• the present invention provides a method for
• determining a property of a formation material in the course of a jet drilling operation, wherein a fluid jet is blasted with erosive power into impingement with the formation material the method comprising the steps of:
• Jet drilling with a high pressure fluid jet is for example very sensitive to rock permeability and porosity.
• a high pressure fluid jet erodes the rock material by impingement on the rock material. Above a certain bit or nozzle pressure drop threshold, the pores in the rock are blown up by the high velocity of the fluid jet. Porous and permeable formation materials such as sandstones or limestones can be jetted away easier than non-porous and non-permeable materials such as shale. This allows to obtain a direct indication of formation material
• the fluid jet is an abrasive fluid jet comprising abrasive particles. In this case, even more information on formation material
• abrasive particles interact differently with the formation material than a high pressure jet of fluid without abrasives.
• Abrasive particles exert a destructive effect on the rock due to the kinetic impact thereof.
• the volume removal rate caused by this effect increases with the kinetic energy of the abrasive particles, and with the abrasive particle concentration times the flow rate (nozzle pressure drop) .
• There is no threshold to this effect and mechanically soft rock is jetted away easier than hard rock.
• the high velocity jet that erodes based on permeability and porosity of the rock.
• By varying the erosive power of the jet it can e.g. be detected whether a soft impermeable formation is drilled, a porous medium strength rock, or a hard and tight rock.
• concentration of abrasive particles in the fluid jet is different between the at least two settings of erosive power.
• concentration of like particles such as steel shot in e.g. an aqueous liquid can conveniently be defined in terms of volume% of the fluid mixture, but in any event and independent of the precise constitution of abrasives in terms of wt% of the fluid mixture. It is ultimately the weight of particles impinging on a certain area of the formation material that is relevant for the kinetic energy. So two, or optionally more, settings of weight concentration of abrasive particles give insight into the dependence of volume removal rate of the
• At least one of a fluid pressure, pressure drop over a jet nozzle, or velocity of jetted fluid is different between the at least two settings of erosive power.
• These parameters relate to fluid velocity, which has an influence on the erosive power of the liquid component of the jet alone, but also on the kinetic energy of abrasive particles when present.
• a classification of hardness of the formation material is obtained.
• Such classification can be a relative, qualitative or semi-quantitative parameter, such as relatively soft versus relatively hard, or classifying a plurality of formation materials encountered in the course of drilling a hole into the subsurface .
• the method can comprise determining one or more of a porosity, a permeability, and/or a tensile strength. Tensile strength is a measure of hardness.
• the at least one property can comprises a rock type. This can e.g. be the case when a characteristic combination of other parameters is found, that can be found in a database; or can be
• the postulated relationship can be qualitative, semi ⁇ quantitative or quantitative.
• it includes the erosive power of hydraulic liquid and the erosive power of abrasive particles, and the at least two settings of erosive power are selected such that the effect of changing only erosive power of hydraulic liquid and/or only erosive power of abrasive particles can be determined individually, i.e. the influence from both effects can be separated in the analysis of the
• an increase of removal rate per increase of kinetic energy of abrasive particles is determined for abrasive jetting.
• the removal rate can in particular be a volume removal rate, which can be calculated from the rate of penetration (depth per unit of time) times the cross sectional area of the borehole that is being drilled. (Velocity times cross sectional area gives volume per time.) Mass removal rate is less practical as it also includes the density of the rock which is another
• the at least one property of the formation material is a material property that is independent of a drilling or excavation method used for accessing the formation material.
• the at least one property of the formation material is a
• the material property is thus not a formation property, i.e. a not a property that is characteristic for a physical parameter in an, typically extended, subterranean formation, for example a formation pressure.
• the material property is characteristic for the material regardless whether it is in the formation or whether it has been removed from the earh formation to surface and ambient conditions.
• the material property is characteristic for a sample of the material of for example less than 1000 kg, or less than 100 kg, or less than 10 kg.
• Figure 1 shows a comparison of the clean water penetration rates in dependence of bit pressure drop for several types of rock material
• Figure 2 shows typical jet drilling performance for sandstone at constant flow rate, with and without
• Figure 3 shows typical jet drilling performance for sandstone at constant nozzle cross-section, with and without abrasives
• Figure 4 shows jet drilling performance for sandstone at constant nozzle cross-section, for various reasons
• Figure 5 shows jet drilling performance with and without abrasives for several types of stone.
• volume removal rate of formation material in dependence on at least two settings of erosive power, it is possible to deduct one or more properties of the material being eroded by the jet.
• volume removal rate of an abrasive jet depends on the particle concentration. It appears that the volume removal rate is proportional to said particle
• concentration at least up to a certain concentration, which was e.g. found to be less than 4 wt% of steel shot in water. Also, the removal rate appears to be
• permeability of formation material may be established on the basis of said predetermined relationship. Also the tensile strength may be established, which properties once known all play a role in determining the formation material which is being drilled.
• the predetermined relationship between the removal rate and the nozzle pressure drop of the high velocity jet, in the absence of abrasive particles, may be given in the form of a graph the horizontal abscissa of which represents the pressure drop and the vertical ordinate of which represents the volume removal rate, said graph furthermore comprising lines which are indicative of the relationship between these ordinates for particular formation materials, such as sandstone, limestone, marble and schist.
• Such graph may be presented in digital format in a logic evaluation device.
• a high pressure water jet can blow up the pores if the rock is porous and permeable.
• the nozzle pressure drop that drives the jet should exceed a certain threshold pressure, dependent on rock type, before rock destruction by this process can occur. Beyond this threshold pressure the rock
• the volume removal rate of a water jet without abrasive particles is proportional to the hydraulic power, which is determined by bit pressure drop. Doubling the hydraulic power of the jet above a certain threshold by doubling the bit
• the volume removal rate is defined as the penetration depth times the cross
• Figure 2 shows Volume Removal Rate VRR in arbitrary units as a function of bit pressure drop in bar in a typical porous sandstone, and at constant water flow though the bit nozzle, for a) a high pressure fluid jet without abrasives; b) the effect of abrasives alone, and c) the combined effect of high pressure fluid jetting and abrasives.
• the threshold pressure P_t is indicated as well .
• Figure 3 shows Volume Removal Rate VRR in arbitrary units as a function of bit flow rate BFR of water in arbitrary units, for a typical porous sandstone, and at constant nozzle flow area (constant nozzle diameter) , for a) a high pressure fluid jet without abrasives; b) the effect of abrasives alone, and c) the combined effect of high pressure fluid jetting and abrasives.
• the bit flow rate corresponding to the threshold pressure P_t is indicated as well.
• Figure 4 shows the influence of different abrasive particle concentrations on the curves c) from Figure 3.
• Curve a) contains no particles (corresponding to curve a from Figure 3), and shows the threshold pressure.
• Curves b) , c) , d) , e) contain respectively 1, 2, 3 and 4 vol% abrasive particles (steel shot) content in water. The higher the abrasive particles content, the greater the removal rate is.
• the influence of the abrasive particles on hard tight rock is relatively small: the liquid jet has a limited influence due to the presence of cracks in the rock. Soft porous sandstone is readily eroded by the abrasive particles, and also there is some influence of the liquid jet.
• shale for instance, a high- pressure jet without solids does not penetrate or hardly penetrates the rock.
• a jet generated with a nozzle pressure drop higher than a certain threshold value can easily penetrate.
• shale is commonly considered a soft rock and relatively easy to drill using mechanical drills, and likewise there are also soft sandstones .
• the abrasive particle content of an abrasive jet drilling bit can distinguish e.g. between a soft impermeable formation material, a porous medium strength rock, or a hard and tight rock.
• a single curve or a plurality of curves in one of the Figures, or equally well a mathematical expression describing the curve (s) can be regarded as a relationship between erosive power (on the abscissa of the curves) and a removal rate of formation material (on the ordinate of the curves) .
• Rock formation materials will have a 'fingerprint' for the rate of penetration as a function of abrasive particle concentration and/or bit pressure drop.
• the volume removal rate of abrasive jet drilling bits is proportional to the hydraulic power and abrasives concentration at the bit.
• Hard rock is harder to drill than soft rock, but doubling the hydraulic power or the particle concentration in the jet(s) leads to twice the volume removal rate.
• Only beyond a certain abrasive particle concentration of typically 4 % by volume (steel shot in water) the particles start losing some of their impact energy through intra-particle collisions and the volume removal rate is not proportional anymore to the abrasive particle concentration.
• the abrasive particles destruct rock by their high velocity impact.
• the volume removal by this abrasive jet drilling (AJD) process is proportional to the kinetic energy in the abrasive particles, i.e. proportional to (abrasives concentration) * (flow rate) * (nozzle pressure drop), and there is not threshold.
• the amount of kinetic energy in the particles in the jet(s) can be varied by varying the hydraulic power that drives the jetstream(s)
• W (Nozzle pressure drop) x (flow rate)
• a high pressure abrasive jet can blow up the pores if the rock is porous and permeable.
• the nozzle pressure drop that drives the jet should exceed a certain threshold pressure before rock destruction by this process can occur. Beyond this pressure the rock destruction is proportional to the nozzle pressure drop minus the pressure threshold.
• volume removal rate without particles is minimal. But shale is also relatively soft: the volume removal rate for abrasive jetting drilling AJD is typically relatively high. Porous sandstone or porous limestone can be jetted by high pressure jetting HPJ (without abrasives), giving a certain P_t pressure and HPJ volume removal rate. Sandstone is typically not very strong, so the volume removal rate by AJD can be
• Tight hard rock e.g. limestone, granite, bassalt
• Conducting a jet drill operation can be generally done as knows in the art. Suitable abrasive jet drill heads, systems and methods of operation are e.g.

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• 2010
  • 2010-12-22 EP EP10796062A patent/EP2516790A1/en not_active Withdrawn
  • 2010-12-22 CN CN201080058367.9A patent/CN102686822B/zh not_active Expired - Fee Related
  • 2010-12-22 AU AU2010334864A patent/AU2010334864B2/en not_active Ceased
  • 2010-12-22 WO PCT/EP2010/070493 patent/WO2011076848A1/en active Application Filing
  • 2010-12-22 BR BR112012015436A patent/BR112012015436A2/pt not_active IP Right Cessation
  • 2010-12-22 CA CA2784989A patent/CA2784989A1/en not_active Abandoned
  • 2010-12-22 US US13/517,285 patent/US20120255781A1/en not_active Abandoned

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