Method for hydrocarbon reservoir monitoring

METHOD OF MONITORING OIL TANKS

The present invention relates to a geophysical trace of the physical properties of the subsurface. More particularly, the present invention involves the injection of tracer fluids for the purpose of monitoring the subsequent distribution and migration of the tracer in a reservoir filled with a hydrocarbon as a means for studying the properties and liquid content of, and the movement of the liquid in. The reservoir.

The ability of the geological formation to promote the passage of fluids depends on the size of the pores, their connectivity (permeability) and the properties of the fluid. The effective permeability also depends on the relative saturations of the various fluids in the pores. In hydrocarbon reservoirs, permeability affects the flow path of formation fluids and fluids injected respectively into the reservoir. It is essential to know the permeabilities of the reservoir to optimize production strategies.

Several tests were carried out to trace the flow of fluid in the reservoir using plotters placed in injection wells and detected during production. US Patent No. 6,645,769 describes this technology. The use of these methods is restricted by the fact that tracers can only be detected in the production well and at least two wells must be drilled.

Other methods propose the use of the acoustic properties of injection fluids in order to trace their spatial distribution over time (US Patents Nos. 4,479,204; 4,969,130; 5,586,082; 6,438,069). Such methods are restricted by the fact that acoustic properties are not always considered a reliable measure of liquid composition.

The object of the present invention is to overcome the problems which arise with the methods mentioned above by injecting the tracer fluid (s) into a hydrocarbon reservoir which can be detected by resistivity measurement techniques as a means. to study the properties and liquid content, and liquid movement in the tank. The tracer fluid (s) may be any fluid having a conductivity different from that of the fluids in the reservoir.

The method is used to monitor and study the properties and / or the geometric extent of a geological formation and / or fluids therein. The method involves injecting fluid or fluids into at least one borehole. This fluid or fluids injected will have a resistivity which will contrast with the geological formation and / or the fluids of the formation and / or will modify the resistivity of the formation or fluids of the formation. The changes that result from the injection of the fluid or fluids will be plotted using resistivity tracing techniques. Several resistivity tracing techniques are available for this purpose. In the final step, the data is interpreted.

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General resistivity tracing techniques are described, for example, by US patents under nos. 4,617,518, 4,633,182; 5,770,945; 6,603,313; 6,842,006 and 6,717,411. Remote intermittent resistivity studies have previously been used for environmental and engineering studies 8Loke, Μ.Η 1999: (Electrical imaging studies for environmental and engineering studies). Tracing of injected conductive / esistive solutions has been used in the evaluation of groundwater flow models (Aaltonen, 2001 .ل: soil control through resistivity measurements in glacial terrain; Parc, s. 1998 : Migration of the liquid in the zone unsaturated with water by the 3D inversion of the resistivity monitoring data; (American patent under n٥ 5, 825,188). A method for tracing combined surfaces and boreholes for reservoir monitoring purposes is disclosed in U.S. Patent No. 6,739,165. Intermittent resistivity monitoring equipment is disclosed in WO 03/023452. A more general description of remote resistivity studies suitable for tracing an injected conductive / resistive fluid is presented by Kaufman and Hoekstra (Kaufman A. A., and Hoekstra, P., 2001: Electromagnetic surveys. Elsevier).

Techniques used for tracing the resistivity of the formation, formation fluids and / or injected fluid (s) can be remote, direct, or a combination of both. They can be applied in the frequency domain or the time domain. The methods can include, but are not limited to performing resistivity tracing using electromagnetic, magnetotelluric, source-controlled galvanic methods, or any combination of these. Data can be gathered by aerial survey, land-based measurements and / or sea-based measurements. Data collection can also be undertaken in the subsurface using detectors placed in one or more boreholes. The source of the electromagnetic, electric or magnetic field can be airborne, land-based or offshore, or placed in the borehole. The borehole and / or well shielding can also be used as a source, or part of a source. Any combination of source and receiver location is possibly possible.

The tracer is an injection fluid with an electrical resistivity that contrasts with the formation and / or formation fluids. The injection fluid or fluids may also be capable of altering the resistivity of the formation or fluids of the formation by biological, chemical or physical means. The resistivity of the fluid or fluids injected can be changed over time to allow tracing of liquid movement with the formation.

The distribution of liquid injects at a precise time or intervals is detected and plotted using remote and / or direct resistivity tracing techniques well known in geophysics. Electrical resistivity is a parameter that strongly depends on the type of liquid. Resistivity tracing has been used for hydrocarbon prospecting as described in US Patents 4,617,518; 4,633,182; 6,603,313;

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5,770,945; 6.842.006 and 6.717.411. Its use for tank monitoring purposes is described in US Patent 6,739,165.

The method can be used after at least one borehole has been drilled in the formation. The method can include resistivity observations on the formation prior to injection, although this is not essential. In addition, the injected fluid (s) or the mixture of injected fluids and formation fluids may be ignited. By plotting the resistivity once or at selected intervals during and / or after injection, the flow path of the injected fluid or fluids and hence the permeability structure and fluid content of the formation can be determined. The resistivity or other properties of the injected tracer fluid (s) may change over time.

The method of monitoring and performing resistivity tracing may involve data processing, migration, modeling and / or inversion. Intermittent data can be processed by joint inversion and / or joint processing of resistivity data collected at different intervals.

Seismic, gravity, magnetic and other geophysical data, in addition to geological data, production, reservoir modeling and reservoir simulation data can also be used in any combination with resistivity measurements to plot the distribution of the fluid or fluids injected or its alteration effects. This assumes the use of data before, during and / or after resistivity plotting.

It is well known that seismic surveys fail to detect the properties and distribution of liquids, while these properties are best detected by resistivity studies. The tracing approach according to the invention thus has considerable advantages compared with the existing methods.

Uses of the invention include:

1) monitoring the distribution of liquid in a hydrocarbon tank, before and during production.

2) evaluation of fluid content (including saturation) structure of porosity and permeability of a reservoir filled with hydrocarbon or similar reservoir.

Example

An example of a typical use of the present invention would be in the production of hydrocarbon for enhanced recovery purposes. In this case, the injection fluid could be, but not limited to solutions of hydrochloric acid (HCl) and / or sodium chloride (NaCl) in water which is very conductive. The injection of this tracer fluid (s) into a reservoir gives a high contrast in resistivity with respect to the surrounding formations and the hydrocarbons in the reservoir. These resistivity contrasts can be identified using the appropriate resistivity tracing methods, including

ΜΑ 28993Β1 including existing ones. For example, it is possible to use controlled source electromagnetic sounding where a horizontal dipole antenna and a set of electromagnetic field receivers are placed on the ocean floor or in any other suitable configuration of acquisition configuration. Likewise, resistivity contrast can be identified by placing one or more dipole antennas and / or one or more receivers in wells. There are a number of different configurations that have the potential to identify resistivity contrasts and the idea is flexible to different installations. By studying the propagation of the tracer fluid (s), it is possible to estimate the parameters of the reservoir, including movements of oil, liquid content, permeability, porosity, etc. There may be other advantages of injecting the tracer fluid (s) such as better recovery through improved secondary permeability and porosity.