№ 9 (September 2006)
IMCP-20-Series Multichamber Samplers Provide PVT-research Credibility
High demand for Russian oil and gas in foreign markets prompts both the state and private-owned Russian vertically integrated oil companies to enhance exploration and field development in new regions, such as Yamal, Gadyn Peninsula, Eastern Siberia, Yakutia and Far East.
By Grigory Pavlenko
Understanding the importance of input data credibility, leading Russian oil companies, such as LUKOIL, Surgutneftegaz, TNK-BP, etc., purchase expensive software, build state-of-the-art R&D centers and supply them with the newest research equipment. At the same time it should be noted that availability of the most up-to-date PVT research equipment and software to process the results does not guarantee credibility in determining rheological and PVT properties when analyzing downhole samples of hydrocarbons.
The main reason for such low credibility of PVT research of fluids and gases is the use of outdated mechanical self-contained samplers with hydraulic timer, such as VPP-300, PG-100 (1000), designed in early 1960’s by the VNIIneft research institute. Despite the fact that these devices do not meet the requirements of STO.153-392-002-2003 standard and do not exclude the human factor influence on credibility and quality of sampling, they are still being used in Russia and CIS countries.
The main drawbacks of the VPP-300 and PG-1000 mechanical hydraulic samplers are as follows:
– absence of technical means for objective and documented date control, operation time measuring and sampling site depth as well as of systems for registering thermobaric fluid and gas parameters both at the time of sampling chamber infill and along the well bore at tripping operations;
– absence of technical capability to simultaneously or non-simultaneously obtain two, three and more independent samples of fluid or gas at single lowering, with several sampling chambers being simultaneously or non-simultaneously filled;
– impossibility of prompt “reprogramming” of the valve unit control mechanism and its “recharging” to sample from different objects in the same well or in different wells during a single exploration trip to the oilfield.
Unfounded fallacies are the statements of some PVT-researchers that the use of substandard samples with recombination technology, but without information on the value of P, T and H (depth) at the sampling chamber infill, will allow them to determine the actual value of gas-oil ratio, bubble-point pressure and other rheological properties of oil and gas, thus leading them to reservoir condition. The reason for such statements is likely to be the absence of facts for comparison at those researchers’ disposal. For many years, they have studied mainly substandard samples and hardly ever had two or three downhole samples obtained under steady-state inflow behavior at the same depth in the drainage interval top, under valid values of sampling site temperature and pressure as well as at simultaneous infill of several sampling chambers.
The newest results of downhole samples analysis obtained by means of VPP-300 or PG-1000 samplers prove it to be next to impossible to receive identical results for two or three samples, taken at different times but in the same depth interval, with the required 1.5 percent tolerance (dispersion) of reservoir oil PVT parameters. Such deposit sampling results run into inacceptable dispersion of scores of percent. The sampling invalidation is 90 percent connected with technical imperfection of the sampling equipment due to absence of instrumental documentary control of downhole sampling operations. The downhole sampling quality completely depends on subjective human factor, namely professionalism and integrity of a lab operator. Downhole sampling is generally performed in the area of fluid double-phase state. At the same time, there is no objective information as to on which depth, at which pressure or temperature it is performed.
Absence of comparability of physicochemical parametres and PVT properties of oil, gas and condensate brings uncertainty and subjectivism into determination of oil and condensate composition and parameters as well as into determination of the value of dissolved gas under reservoir conditions.
In many cases, free gas contains much more methane than there actually is dissolved in oil or condensate under natural conditions. Thus, there appears a completely different gas solubility in natural petroleum products, which consequently overvalues gas-oil ratio, volume factor, and shrinkage factor as well as other hydrocarbon parameters to be widely used for assessing reserves and producing development simulation models of an oilfield.
The oilfield experience shows that in the course of development the values of gas-oil ratio, bubble-point pressure and viscosity change considerably causing changes in operation mode of oil-and-gas production equipment and inside the field pipelines as well as in the system of field development as a whole. These conditions force a subsoil user to regularly perform well flow testing and downhole sampling for controlling and studying dynamics and quality of parameters changes in fluid-gas-and-dynamic medium of the reservoir. Also, the subsoil user will have to regularly update development system and stimulation complex in accordance with the oilfield dynamics and conditions.
In the course of reforming the Russia’s oil-and-gas sector, all research institutes and design offices, which delivered equipment, tools and operation technology for well developing, testing and sampling were practically destroyed.
The engineers of Well Flow Test Department of OEG Petroservice found an original solution of a complicated technical task – dataware for qualitative and instrtumental control of well testing and sampling. The company developed, patented and introduced into full-scale production a brand new universal technology of downhole leakproof sampling for fluids and gases as well as the IMCP-20 multichamber downhole samplers, self-contained software-programmable and remotely controlled devices of both suction and flow types.
At a single lowering these samplers allow for lengthy thermobaric condition control (well flow testing) along the well bore and at the bottom. The samplers also provide an opportunity for downhole sampling with one or several independent sampling chambers, thus excluding (or controlling) the influence of human factor.
The IMSP-20 samplers allow for continuous registration of actual calendar time, temperature, pressure, depth (by means of collar locator or gamma-ray logging) and sampler location when lowering, pulling or at the sampling site.
To provide continuity of internal and external lab processing of the IMCP-20 sampling chambers, all the outer sampling chamber connections are compatible with VPP-300 or PG-1000 that causes no difficulty in unloading the chambers.
The downhole samplers by OEG Petroservice can be lowered down by means of tubing, scratch wire or logging cable.
When the IMCP-20 sampler is in the well, the information is recorded continuously into its nonvolatile memory or translated to the surface through logging cable both at lowering and pulling of the downhole device. At that, the moment of opening and quality shutting of every sampling chamber is registered independently at the sampling site. The parameters to be registered include calendar time, temperature, pressure and lowering depth as per colla r locator or gamma-ray logging data. All the recorded information is pegged against actual calendar time (year, day, hour, minutes, seconds), read out and visualized at the mobile PC directly at the well site right after pulling the device to the wellhead. Along with the ability of obtaining two, three and more independent leakproof samples of fluid or gas, the device can stay downhole for a long time and register at the point of pressure transient (PTT) and temperature transient within three to 30 days before or after sampling. Preset time or pressure programming of the opening moment is individually performed for every sampling chamber with the help of mobile PC right before lowering the sampler. One electronic module of the sampler is able to control the operation of one or two valve mechanisms.
The sampler is of modular design, so the number of sampling chambers lowered down at the same time is only limited by the height of a sluice chamber, which is used in lubricator operation.
At the well site, right after the sampler has been pulled to wellhead, the information on every sampling chamber (P, T, H, t) is transferred to a mobile PC in the form of graphs and tables, where sampling quality is assessed and sampling technology is controlled. The device design allows for valve actuating gear recharging and reprogramming at the well site. That provides the possibility to perform one or several samplings at a number of wells, at various depth, temperature and pressure intervals with the help of a single electronic unit, thus avoiding the necessity to return to the base. All the above mentioned is practically impossible to carry out with the help of VPP-300 or PG-100 (1000) samplers. The sampler is optionally delivered complete with two-four spare sampling chambers, special metal container for transporting the equipment to the well site and a leakproof case for transporting the sampling chambers filled with pressurized fluid or gas to the research lab. If necessary, a special-purpose mobile table for sample unloading is delivered as well as thermostatic (air) unit and the MP-600 (1200) hydraulic press to calibrate and test temperature and pressure gauging channel of the sampler. All the above mentioned is optional.
The results of downhole oil sampling, obtained by IMS-20 and analyzed at the Center for Core Sample and Reservoir Fluids Research of KogalymNIPIneft, proved complete identity of the samples, received from the four chambers. The composition and quantity of dissolved gas and bubble point pressure value showed practically no difference between the chambers. Such convergence on the four samples has not been recorded in this research center for five years.
The IMCP-20s, multichamber downhole samplers, self-contained software-programmable and remotely controlled devices of both suction and flow types, are manufactured in several modifications for the limiting temperature of up to 125-145 C and pressure of up to 100 MPa. IMCP-20 is also authorized for industrial application at oil and gas enterprises by RF State Mining and Technical Inspectorate (Gosgortekhnsdzor). Certificate of conformance to specifications and GOSTs (Russian Standards) is available.
At present, the IMCP-20 multichamber sampler is a unique multifunctional device for well testing, well flow testing, and sampling. It has no direct counterpart both in Russia and abroad, that is why this equipment is widely used at the oilfields of Western Siberia. Russian operators and geophysical companies, such as LUKOIL, Gazprom, MGK ITERA, KNGF and others are actively employing these samplers.
IMSP-20 samplers are also used by foreign companies and joint ventures, such as SPD N.V. (Shell) and SP AIK, at the oilfields in Russia.