Simplified ultrasonic damage detection in fluid filled pipes

\u3cp\u3eThe location and extent of damage in a pipe can be remotely determined from weld and internal damage reflections using a single acoustic emitter/sensor pair. The use of normalised reflections yields single numbers enabling long distance data collection techniques such as wireless hopping. The attenuation is twice as high for opposite inner and outer fluids (whether air and water, or water and air) as compared to identical inner and outer fluids. The absolute recorded signals in the water-filled pipe are attenuated by a factor two compared to the empty pipe. The axial length of detection is reduced by a half. The reduction of >90% in sensors and the longer axial detection (>10× current state-of- the-art- technology) means that permanent fixed sensor pairs for whole pipelines are on the horizon of possibility. The greatest advantage is envisioned in submersed pipelines.\u3c/p\u3

Damage detection through pipe bends

Axial pipeline defects are detectable from torsional guided wave reflections through 90 deg elbows. This paper demonstrates that detection of localized damage in carbon steel pipes with a so-called standard long and very long radius elbow is possible using a single permanently installed source–receiver pair. We use dispersion imaging to determine why this is not possible in a short radius elbow pipe. Although the remote damage is detected in a standard short radius bend pipe, there is not enough signal to detect localized damage. Since pipeline bends are normally of at least standard long radius, the acoustical behavior is similar to that previously determined in straight pipes. The reflective method can thus be applied fruitfully to monitor structural health beyond industrial pipeline bends

Dispersion and attenuation by transmission, reflection, and mode conversion in welded pipes

Torsional wave dispersion and attenuation in an open empty welded pipe are determined from a multi-receiver position reflection experiment. The fundamental torsional wave is dominantly reflected at the free end and the converted non-axisymmetric flexural modes are naturally attenuated. The resulting phase velocity contours are in agreement with theoretical predictions. The transmission losses are quantified and compared to those reflective elements associated with end and weld reflection. At any reflective node, the incident wave is split between back and forward preserved mode scattering (“reflection/transmission”), conversion to other modes plus energy lost by absorption. The ratios for each element are quantified

Permeability thickening fluids for improved secondary oil recovery

Waterflooding is limited by zones of spatially varying permeability which cause channelling. More crude oil could be produced by a more uniform water/brine front across layers of different permeabilities. Novel non-polymeric water additives (CTAB+NaSal in brine) are used to selectively slow down flow of water in high permeability zones. In order to isolate rheological effects from rock fluid interactions, we have carried out experiments on inert glass cores. A monotonic increase of viscosity as function of permeability is observed for the range 45–2200 mD (covering typical reservoir ranges). This effect can be referred to as permeability thickening. This result opens up the possibility of tunable fluid engineering for any given permeability distribution of reservoirs. Low additive concentrations

Wellbore to fracture proppant-placement-fluid rheology

Novel reservoir engineering displacement fluids (cetyltrimethylammonium bromide and sodium salicylate in water) are examined as candidates for proppant placement during fracturing. The need for additional crosslinkers, breakers or contact with hydrocarbons to change the viscosity is eliminated. These materials have a viscoelastic response governed by flow. Two fluid compositions are investigated in relation to Newtonian fluids of similar base viscosity to determine how shear induced structures (SIS) influence flow properties in the near-wellbore region of a fracture. In Couette flow, the fluid displays shear thickening and thinning within a discrete shear regime. Extensional flow tests in a microfluidic device reveal a flow resistance up to 25 times higher than Newtonian fluids. This extra flow resistance is due to an induced intermicellar network and has potential application for improved proppant carrying after injection via a perforation. Particle image velocimetry is used to visualise the entrance flow in a fracture. Instabilities are reduced as flow through the perforation increases. The viscosity contrast ratio between zero-shear viscosity and maximum viscosity response determines the extra proppant carrying capacity

Gas-solid heat exchange in a fibrous metallic material measured by a heat regenerator technique

The convective heat transfer properties of a porous metallic fibre material used in gas surface combustion burners are studied. The important parameter governing the heat transfer between hot gas and metal fibre—the heat transfer coefficient—is measured using a non-steady-state method based on cyclic counterflow heat regenerator theory. The factors controlling the ranges of experimental conditions that can be used are studied. A correlation between gas flow rate and heat transfer is obtained for laminar flows, showing a rapid increase in heat transfer coefficient with increasing gas flow. The heat transfer coefficient is significantly lower than previously assumed. -------------------------------------------------------------------------------

Sweep enhancers for oil recovery

The use of viscoelastic sweep improvers to overcome injected fluid diversion is assessed at the low pressure gradients associated with secondary oil production. The flow evolves from Newtonian to non-Newtonian behavior with increasing pressure gradient. Additive concentration determines this transition and controls the effectiveness of selective retardation. This is demonstrated in an experimental simulation of parallel flow in two core samples of different permeabilities. Even at pressure gradients lower than 1.0 bar/m channeling can effectively be reduced and early water breakthrough delayed. This has the potential to greatly increase ultimate oil recovery

Improved oil reservoir sweep with viscoelastic surfactants

Viscoelastic surfactant solutions increase oil recovery by selectively modifying the viscosity of the injected displacing fluid in different zones of the reservoir. We demonstrate that flow resistance in high permeability zones is increased whereas no significant change in viscosity occurs in low permeability zones. This greatly reduces injected fluid losses via the high permeability route. In two phase flow in sandstones, recovery increases by about 25%. Efficiency also increases by a factor of 3 as shown by the large reduction in injected volume at breakthrough. Consequently less fluid is lost through high permeability thief zones. Recovery is increased in carbonates as well but the efficiency is depleted due to apparent changes in wetting. The reduction in injected fluid before breakthrough has the potential to prolong the economical lifespan of water wet reservoirs

Viscoelastic surfactants for diversion control in oil recovery

Hydrocarbon recovery is significantly improved in heterogeneous systems by injecting viscoelastic surfactant solutions. These solutions retard the effect of preferential flow through so called ‘thief zones’ (high permeability regions). The viscoelastic fluid passively increases flow resistance in regions of high permeability thereby partially blocking thief-zones. The low permeability volume paths in these heterogeneous reservoirs are swept more efficiently since less of the injected flooding fluid is lost. The produced water cut is significantly reduced which increases the overall effectiveness of the recovery process. The solutions we used are self-regulating, making them universally applicable without extensive knowledge of the reservoir properties

Enhanced viscosity reduction in heavy oils by subcritical water

\u3cp\u3eWe determine the chemical changes associated with viscosity reduction when heavy oil is cracked in subcritical water. The viscosity reduction has a temperature threshold for onset of 290 °C—this suggests an enhanced acid cracking regime associated with the maximisation of water dissociation at these conditions aided by the already increased solubility. The mean molecular weight is reduced by nearly 50%. Oxygen and sulphur are reduced by about half of this—either by expelled gas effluent (H \u3csub\u3e2\u3c/sub\u3eS) or by conversion into mono-aromatic base sulphur-containing structures. The amount of lower branched paraffins is increased.\u3c/p\u3