FIELD

The invention relates to an inflow indicator apparatus for a well in an underground structure, in which at least one tracer depot is arranged to be in contact with a partial fluid flow flowing from a producing structure into the well. A method of monitoring the inflow of a partial fluid flow from a producing structure into a well in an underground structure is described as well.

BACKGROUND

When monitoring the inflow into a production tubing from different production zones in an underground well, for example a hydrocarbon well, it is known to use tracers that are dissolved in the fluid flowing into the well and up through the production tubing. Tracers of different characteristics are often used in order to enable the formation of a picture of the inflow situation in different parts of the well. Typically, different types of tracers are used at different locations in the well to provide an overview of the inflow into different parts of the well, and tracers which can provide indications of what is flowing in to the different parts of the well, especially of whether a structure is only producing formation water, are used, by tracers reacting differently on contact with a fluid type being used, for example tracers that are dissolvable only in contact with water, but non-dissolvable in contact with hydrocarbons. Tracers can also be used to give an indication of whether decreasing inflow is due to beginning formation of deposits in the openings of the production tubing, or whether the decreasing inflow is due to the reservoir being in the process of being depleted.

The tracers are placed in apparatus that is lowered into the well before the measuring starts. The apparatus may constitute a permanent part of the well installation, for example in the form of a sand screen with integrated tracer depots in a production tubing, or the apparatus may have as its sole function to contain the tracers. The tracers are preferably formed as dissolvable salts that are typically contained in pores in a porous, non-dissolvable block material positioned in contact with the fluid flow passing through the apparatus. The tracers are thereby released gradually and over a long time.

It is a problem to provide a good overview of the inflow into a well from different production zones when the accumulated fluid flow is coming into contact with the tracers in all the portions of the well, that is to say all the production zones in the well.

US2011239754A1 discloses a system and a method for indicating inflow of water in a well producing hydrocarbons. Tracer depots that are dissolved by water, but not by hydrocarbons, are placed in the well by, for example, being arranged on downhole well components or casing at a production zone, being pumped into the well as part of a mixture which is used to prop a structure or as a gravel pack, for fracturing the structure, et cetera, or is forced into a structure surrounding the well in a perforation operation. The presence of a tracer in the production fluid from the well is registered by a sensor system with several sensors arranged at different locations in the well, the sensors being connected to a processing system at the surface via a communication line extending up through the borehole. Even though different production zones are isolated from each other by means of isolation devices, for example packers, the document teaches nothing about how production fluids from a production zone are prevented from coming into contact with tracers in a production zone lying above (downstream).

From US2015176396A1 a system and a method for estimating fluid flow rates for each one of several separate production zones in a multilayer reservoir to a well extending through the reservoir are known. Distinct tracer sources are placed in known positions in the inflow path of each inflow zone, which is defined from a so-called reservoir base line in the well by means of an entry point. The entry points may be provided by holes, openings in a completion, a pipe or a screen, or be provided as a valve. The tracers may have been placed in the reservoir during completion of the well or in well equipment, which has been installed in the well or reservoir later. The tracers may further be placed in the reservoir formation, in a completion, a casing, a liner or in equipment arranged in the well. The inflow zones represent completion zones, which are separated from each other by means of flow isolation (packers). It cannot be deduced how an inflow indicator apparatus may be constructed.

SUMMARY

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.

The object is achieved through the features that are specified in the description below and in the claims that follow.

The invention relates to an apparatus arranged to be placed at a production zone in a well in order to, by means of the release of one or more tracers, be used in monitoring the inflow of fluid into the well from said production zone without the tracers being affected by a fluid flow from production zones upstream (downstream) of said production zone. The apparatus comprises a tubular body which is placed in a through flow path for production fluids, forming an annulus encircling the tubular body. The apparatus is provided with a settable seal, which is arranged to close to the flow of fluids in the annulus between first and second end portions of the apparatus. A wall encircling the tubular body is typically an internal wall of a portion of a casing, but is not limited to that kind of pipe. The wall may also consist of a borehole wall. The apparatus is provided with at least one tracer depot arranged on the periphery of the apparatus between said seal and one end portion or both end portions of the tubular body.

The tubular body of the apparatus may have a length, which is adapted to the extent of the inflow portion of the well for a production zone, the apparatus extending substantially along the entire inflow portion. The length of the tubular body may also be considerably smaller than the extent of the inflow portion in the axial length of the well. Fluid entering the well from said production zone is kept separated from the fluid flowing from other, upstream production zones of the well, until the partial fluid flow reaches the open end portion(s) of the annulus, where the partial fluid flow mixes with the fluids flowing from other, upstream production zones in the well, also termed the main fluid flow. By the very fact of said annulus being closed by means of the seal, fluid flowing out of the well from production zones upstream (downstream) of said production zone will not be able to flow through said annulus and come into contact with the at least one tracer depot in the apparatus. Correspondingly, fluid that is flowing out of other production zones will only come into contact with a tracer depot/tracer depots in a respective apparatus placed at each of these production zones.

The invention is defined by the independent claims. The dependent claims define advantageous embodiments of the invention.

In a first aspect, the invention relates more specifically to an inflow indicator apparatus for a well in an underground structure, in which at least one tracer depot is arranged to be in contact with a partial fluid flow flowing from a producing structure into the well, characterized by the inflow indicator apparatus comprising a tubular body and a seal encircling a portion of the tubular body, the at least one tracer depot being arranged externally on the tubular body, and the seal being settable against an encircling wall, and the tubular body, the seal and the encircling wall defining an annulus forming a first flow path for the partial fluid flow which is separated from a second flow path through the inflow indicator apparatus for a main fluid flow formed of a through fluid line in the tubular body, the first flow path extending from the seal to an end portion of the tubular body.

The seal may encircle a first end portion of the tubular body. Alternatively, the seal may encircle a middle portion of the tubular body.

The first end portion may be arranged upstream in the well. Alternatively, it may be arranged downstream in the well.

The tubular body may exhibit a length considerably smaller than an axial extent of an inflow portion for the producing structure in the well. Alternatively, the tubular body may exhibit a length substantially equal to the axial extent of the inflow portion for the producing structure in the well.

The encircling wall may be a pipe wall, typically a casing wall. Alternatively, the encircling wall may be a well wall defining a borehole against the underground structure.

In a second aspect, the invention relates more specifically to a method of monitoring the inflow of a partial fluid flow from a producing structure into a well in an underground structure, characterized by the method comprising the steps:arranging an apparatus according to the first aspect of the invention at the producing structure,forming a first flow path for the partial fluid flow in an annulus between the apparatus and the encircling wall from an inflow portion from the producing structure by defining the annulus by setting a seal against the encircling wall, in order thereby to prevent the flow of a main fluid flow in the annulus,letting the partial fluid flow be brought into contact with at least one tracer depot arranged externally on the tubular body,directing the partial fluid flow into the main fluid flow at an end portion of the tubular body,directing an accumulated fluid flow out of the well, andregistering the contents of tracers released from the at least one tracer depot into the partial fluid flow.

