Ramona M. Graves

Phase Behavior and Minimum Miscibility Pressure in Nanopores

Numerous studies indicate that the pressure/volume/temperature (PVT) phase behavior of fluids in large pores (designated “unconfined” space) deviates from phase behavior in nanopores (designated “confined” space). The deviation in confined space has been attributed to the increase in capillary force, electrostatic interactions, van der Waals forces, and fluid structural changes. In this paper, conventional vapor/liquid equilibrium (VLE) calculations are modified to account for the capillary pressure and the critical-pressure and -temperature shifts in nanopores. The modified VLE is used to study the phase behavior of reservoir fluids in unconventional reservoirs. The multiple-mixing-cell (MMC) algorithm and the modified VLE procedure were used to determine the minimal miscibility pressure (MMP) of a synthetic oil and Bakken oil with carbon dioxide (CO2) and mixtures of CO2 and methane gas. We show that the bubblepoint pressure, gas/oil interfacial tension (IFT), and MMP are decreased with confinement (nanopores), whereas the upper dewpoint pressure increases and the lower dewpoint pressure decreases.

Laser spallation of rocks for oil well drilling

Laser rock spallation is a rock removal process that utilizes laser-induced thermal stress to fracture the rock into small fragments before melting of the rock occurs. High intensity laser energy, applied on a rock that normally has very low thermal conductivity, concentrates locally on the rock surface area and causes the local temperature to increase instantaneously. The maximum temperature just below the melting temperature can be obtained by carefully controlling the laser parameters. This results in a local thermal stress in subsurface that is enough to spall the rock. This process continues on a new rock surface with the aid of the high pressure gas purging blowing away the cracked fragments. Laser parameters that affect the laser spallation efficiency will be discussed in the paper. Also reported in the paper is the multi laser beam spot spallation technique that has been developed for potentially drilling large diameter and deep gas and oil wells.Laser rock spallation is a rock removal process that utilizes laser-induced thermal stress to fracture the rock into small fragments before melting of the rock occurs. High intensity laser energy, applied on a rock that normally has very low thermal conductivity, concentrates locally on the rock surface area and causes the local temperature to increase instantaneously. The maximum temperature just below the melting temperature can be obtained by carefully controlling the laser parameters. This results in a local thermal stress in subsurface that is enough to spall the rock. This process continues on a new rock surface with the aid of the high pressure gas purging blowing away the cracked fragments. Laser parameters that affect the laser spallation efficiency will be discussed in the paper. Also reported in the paper is the multi laser beam spot spallation technique that has been developed for potentially drilling large diameter and deep gas and oil wells.

Rock perforation by pulsed Nd:YAG laser

In gas and oil well completion, perforation channels must be made through the steel casing wall and cement and into the rock formation in the production zone to allow formation fluid to enter the well. This paper will present study results on using a pulsed Nd:YAG laser to drill the perforation channels through reservoir rocks. With fiber optic cable delivery capability, an Nd:YAG laser beam has the potential to be delivered to deep oil production zones. Effects of laser pulse parameters, beam properties, and assistant gas purging on the perforating efficiency and rock permeability will be reported. Unlike the conventional explosive charge perforation that often causes great reduction of rock permeability, laser perforation would enhance the rock permeability, therefore increasing the oil or gas production rate of the wellIn gas and oil well completion, perforation channels must be made through the steel casing wall and cement and into the rock formation in the production zone to allow formation fluid to enter the well. This paper will present study results on using a pulsed Nd:YAG laser to drill the perforation channels through reservoir rocks. With fiber optic cable delivery capability, an Nd:YAG laser beam has the potential to be delivered to deep oil production zones. Effects of laser pulse parameters, beam properties, and assistant gas purging on the perforating efficiency and rock permeability will be reported. Unlike the conventional explosive charge perforation that often causes great reduction of rock permeability, laser perforation would enhance the rock permeability, therefore increasing the oil or gas production rate of the well

Rock removal using high-power lasers for petroleum exploitation purposes

This paper describes the experimental results of selective rock removal using different types of high power lasers. US military owned continuous wave laser systems such as MIRACL and COIL with maximum powers of 1.2 MW and 10 kW and wavelengths of 3.8 and 1.3 mm respectively, were first used on a series of rock types to demonstrate their capabilities as a drilling tool for petroleum exploitation purposes. It was found that the power deposited by such lasers was enough to drill at speeds much faster than conventional drilling. In order to sample the response of the rocks to the laser action at shorter wavelengths, another set of rock samples was exposed to the interaction of the more commercially available high power pulsed Nd:YAG laser. To isolate the effects of the laser discharge properties on the rock removal efficiency, a versatile 1.6 kW Nd:YAG laser capable of providing pulses between 0.1 millisec and 10 millisec in width, with a maximum peak power of 32 kW and a variable repetition rate between 25 and 800 pulses/sec was chosen. With this choice of parameters, rock vaporization and melting were emphasized while at the same time minimizing the effects of plasma shielding. Measurements were performed on samples of sandstone, shale, and limestone. It was found that each rock type requires a specific set of laser parameters to minimize the average laser energy required to remove a unit volume of rock. It was also found that the melted material is significantly reduced in water saturated rocks while the drilling speed is still kept higher than conventional drilling.

Drilling large diameter holes in rocks using multiple laser beams

Studies on drilling petroleum reservoir rocks with lasers show that modern infrared lasers have the capability to spall (thermally fragment), melt and vaporize natural earth materials with the thermal spallation being the most efficient rock removal mechanism. Although laser irradiance as low as 1000 W/cm2 is sufficient to spall rock, firing the beam on a single spot for too long at that intensity causes rock melting and reduces removal efficiency. Also, it is difficult to visualize an efficient way to create a six or eight inch hole by sending one large beam down hole. Alternatives are either to raster the beam to cover the 20 cm hole area or, using a pattern of many small beams illuminated sequentially or in groups, create a nearly circular work face. This paper will present the testing results of the multiple small beam method. The effect on rock removal efficiency of several parameters, including relaxation time between laser bursts, basic patterns of multiple beams, and beam spot overlapping amounts are determined and presented.Studies on drilling petroleum reservoir rocks with lasers show that modern infrared lasers have the capability to spall (thermally fragment), melt and vaporize natural earth materials with the thermal spallation being the most efficient rock removal mechanism. Although laser irradiance as low as 1000 W/cm2 is sufficient to spall rock, firing the beam on a single spot for too long at that intensity causes rock melting and reduces removal efficiency. Also, it is difficult to visualize an efficient way to create a six or eight inch hole by sending one large beam down hole. Alternatives are either to raster the beam to cover the 20 cm hole area or, using a pattern of many small beams illuminated sequentially or in groups, create a nearly circular work face. This paper will present the testing results of the multiple small beam method. The effect on rock removal efficiency of several parameters, including relaxation time between laser bursts, basic patterns of multiple beams, and beam spot overlapping amounts ...

Low-salinity Water-alternate-surfactant in Low-permeability Carbonate Reservoirs

Low-salinity water injected into carbonate cores, which have undergone sea-water injection, can produce additional oil more economically if a low-concentration non-ionic surfactant is added to the low-salinity water and injected as chase fluid. One major reason for the additional oil recovery is that low-concentration surfactant effectiveness favors the low-salinity environment. Several coreflooding, contact angle, and IFT experiments were performed to assess the proposed process. The core flooding sequence includes seawater, low-salinity water, and low-concentration non-ionic surfactant. However, for field application, we proposed low-salinity water-alternate-surfactant injection. The surfactant concentration in low-salinity water was 1,000 and 5,000 ppm. Phase behavior and cloud point measurements were conducted prior to surfactant injection. The core permeability is 0.5 to 1.5 md, and porosity ranges from 0.18 to 0.25. Cores were aged for eight weeks at reservoir pressure and temperature. The pendant drop oil-brine IFT and captive oil-droplet contact angle measurements were performed at variable brine salinity in the presence of surfactant. Seawater and low-salinity waterflooding corefloods yielded ultimate oil recoveries of up to 57 percent. Up to 10 percent additional oil recoveries was obtained from low-concentration non-ionic surfactant in low-salinity waterflood. With decreasing salinity, in presence of 1,000-ppm surfactant, favorable wettability alteration from intermediate-wet to water-wet was observed by contact angle measurements. Moreover, addition of small concentration of surfactant decreased the IFT and altered the wettability of several one-inch diameter, crude-aged, discs to water wet.

Interaction of pulsed CO and CO2 laser radiation with rocks typical of an oil field

Experiments on laser-rock-fluid interactions have been carried out by using pulsed CO and CO2 lasers which irradiated rocks typical for oil field: sandstone, limestone, shale and granite. Energy fluence and laser intensity on rock surface were up to 1.0 kJ/cm2 and 107 W/cm2, respectively. The dependencies of specific energy consumption (i.e. energy per volume needed for rock excavation) on energy fluence, the number of pulses, saturated fluid, rock material and irradiation conditions have been obtained for various rock samples. The dependencies of momentum transferred to the rock on energy fluence for dry rocks and rocks with surface saturated by water or mineral oil have been measured. High-speed photography procedure has been used for analyzing laser plasma plume formation on a rock surface. Infrared spectra of reflectivity and absorption of rocks before and after irradiation have been measured.

Interaction of pulsed CO and CO2 laser radiation with rocks

Experiments on laser-rock-fluid interaction have been carried out by using pulsed CO and CO2 lasers which irradiated rocks typical for oil field: sandstone, limestone, shale and granite. Energy fluence and laser intensity on rock surface were up to 1.0 kJ/cm2 and 107W/cm2, respectively. The dependencies of specific energy consumption (i.e. energy per volume needed for rock excavation) on energy fluence, the number of pulses, saturated fluid, rock material and irradiation conditions have been obtained for various rock samples. The dependencies of momentum transferred to the rock on energy fluence for dry rocks and rocks with surface saturated by water or mineral oil have been measured. High-speed photography procedure has been used for analyzing laser plasma plume formation on a rock surface. Infrared spectra of reflectivity and absorption of rocks before and after irradiation have been measured.

Matrix-Fracture Interface Cleanup Protocol for Tight Sandstone and Carbonate Reservoirs

In tight sandstone and carbonate reservoirs, the hydrocarbon recovery is mainly governed by the matrix- fracture interface mass transfer efficiency. To improve the matrix-fracture interface mass transfer in tight sandstone and carbonate reservoirs, we propose the following protocol to clean up the matrix-fracture interface and improve hydrocarbon production: (1) Inject one of the following – CO2 followed by anionic or non-ionic surfactant, Anionic or non-ionic surfactant followed by CO2, miscible or near miscible CO2 gas, low concentration anionic or non-ionic surfactant. (2) Repeat the process when another cycle of treatment is needed. The same procedure can be applied into injection well to improve injectivity. The proposed cleanup protocol improves production because – wettability alteration, reduction of IFT, swelling of the oil leading to lower viscosity, and molecular diffusion among other thermodynamic effects– all acting at the matrix-fracture interface. To assess the proposed matrix-facture interface clean up protocol, IFT and contact angle measurements that mimic the proposed processes were conducted. Favorable wettability alteration of tight carbonate and sandstone crude-aged cores and oil-brine IFT reduction were observed.

Rock phase control by using high power laser for production enhancements

This study is part of a more extensive research effort by Gas Technology Institute to apply high power laser technology in well construction and completion techniques for the oil and gas industry. It has been demonstrated that by altering laser parameters, including power and duration, changes in rock properties and phase behavior can be controlled. This paper presents the results and analysis of high power laser interactions, including the Mid-infrared Advanced Chemical Laser (MIRACL), Chemical Oxygen Iodine Laser (COIL) and carbon dioxide lasers in limestone, sandstone and shale samples. When laser energy was allowed to melt minerals within the rock matrix, an impermeable barrier with ceramic-like characteristics was created that may provide in-situ fluid flow control and wellbore stability. A porous ceramic barrier could also be created on demand through the application of a high velocity purging system for applications in unconsolidated rock formations, preventing sand production and tunnel collapse, critical concerns in well completion and production operations.This study is part of a more extensive research effort by Gas Technology Institute to apply high power laser technology in well construction and completion techniques for the oil and gas industry. It has been demonstrated that by altering laser parameters, including power and duration, changes in rock properties and phase behavior can be controlled. This paper presents the results and analysis of high power laser interactions, including the Mid-infrared Advanced Chemical Laser (MIRACL), Chemical Oxygen Iodine Laser (COIL) and carbon dioxide lasers in limestone, sandstone and shale samples. When laser energy was allowed to melt minerals within the rock matrix, an impermeable barrier with ceramic-like characteristics was created that may provide in-situ fluid flow control and wellbore stability. A porous ceramic barrier could also be created on demand through the application of a high velocity purging system for applications in unconsolidated rock formations, preventing sand production and tunnel collapse, ...