Introduction

Present invention is a method for a rapid verification of satisfactory clean-up at the end of the completion process when starting production of petroleum fluids while the

completion rig is still at the well location. More specific the method concerns marking of fluids by one or more distinct tracers, in one or more separate zones along the well, before start up of the production, followed by registration of back produced tracers to determine whether all the completion fluid has been back produced and if possible determine which well zones are participating to the production in this early production stage. If the verification is positive the well is satisfactory cleaned up and the completion rig may be removed. If the verification is negative and the problems are

identified one may potentially use the rig to make immediate actions . Problems to be solved

During completion of oil wells and the following clean-up during start up of oil wells, it is very important in an as early a stage as possible to have the control on effectiveness of the clean-up process. The costs of having a rig or a drilling vessel at location during this operation is very high, and may generally come to 3 - 5 mill. NOK per 24 hours. The clean-up process is successful if all completion fluids and particles as cuttings are out of the well and that the anticipated producing zones actually are producing, i.e. oil is flowing into the well in all zones or that it is reasonable to expect that all the zones will generate production. Clean-up is defined as a process where completion fluids and particles are produced out.

The in-flow properties (skin) along the downhole target will change dramatically during this phase. The process may have several purposes, but the most important are:

a) as far as possible to prove that all completion fluid and particles are out

b) as far as possible to verify that the "mudcake" has been broken down, and that the well is flow connected to a desired degree to the reservoir

c) give an indication about the inflow profile

To verify that the clean-up process have given a satisfactory result within a short time, gives the possibility to "release" the rig or the drilling ship at an as early as possible stage and secure that one may not have to carry out clean-up

actions that is both time consuming and gives unnecessary high costs as a result, on a later stage. A verification of the clean-up process may be performed by the use of chemical compounds as for instance substances that may be detected by use of spectroscopic methods as UV, VIS,

Fluorescence, and so on. It is known that produced oil contains different components that may cause interference with the tracers due to its own absorption maxima in the UV and VIS range. The detection methods of today are complicated and time consuming in proportion to the time pressure existing on releasing the rig. WO2010005319A1 describes a tracer system wherein the tracer components comprise polyether alcohol or derivatives thereof. These tracers are special arranged for to be detected in very low concentrations. The method for analysis is complex. US20060144588A1 comprises a portable arrangement for analysis of placed tracers of a certain concentration to an oil well. The analysis is quantitative with regards to concentration. WO0181914A1 describes an intelligent release of tracers to decide where, i.e. in which zones, water, oil or gas flows into the production well, and for following use of that information to possible closing off zones, mapping of

production rates or in other ways controlling hydrocarbons to give a more optimal reservoir exploitation over years.

The publication SPE 135070 "Using Chemical Tracers for Flow Profiling a Subsea Horizontal Well ..." by Bakhshi et al .

describes a study which includes placing different tracers in specific locations along the length of a lower completion. The tracers may be soluble in oil or water. Samples are taken at the surface during a short period of start up. The samples are analyzed to determine presence of tracers. Based on the results and the known placed position qualitative information of the fluid flow in the well is generated. All analysis of tracers are carried out on shore.

The publication SPE "Parmanent Tracers Embedded in Downhole Polyners Prove Their Monitoring Capabilities..." by Fridtjof Nyhavn and Anne D Dyrli describes a well completion with placed tracers along the lower part of the completion. The tracers are designed to change behavior as a function of the surrounding environment. Released tracers are analyzed from samples taken topside and the concentration of the tracers gives information of the well flow. The tracers are soluble in oil. Sampling is carried out over an extended period and all the analysis are carried out on shore and are time consuming, up to a week. The prior art describes methods of collecting well flow information by the use of different types of tracers. The analysis is time consuming and complex and performed in a separate laboratory mostly on shore. Since the day cost of having the completion rig at the well site is very high, to reduce the time of analyzing is essential.

US20050109087 Al describes methods and compositions for determining the source of fluids or particulates for

subterranean formations and the tracer matrix that may be used within such method. Different tracers are to be placed in different zones and the photoactive material used is detected in the return flow. Detection of tracers may be carried out by detection techniques that can measure the absorption or emission of light. Methods referred are by calorimeters, thin layer chromatography, gas chromatography, HPLC, UV-, VIS- , fluorescence- and mass-spectroscopy . Due to the fact that produced oil contains different components that may cause interference with the tracers due to its own absorption maxima in the UV and VIS range detection in oily samples may be difficult. This patent application describes the same

technology and solution as WO0181914 Al above, but has a more detailed description Short summary of the invention

The invention is a method for a rapid verification of

satisfactory clean-up at the end of the completion process when starting production of petroleum fluids while the

completion rig is still at the well location. In other words, the invention is a rapid-verification-of-satisfactory-clean-up method used at the end of the completion process when starting production of petroleum fluids while the completion rig is still at the well location. Stated more briefly, the method is an in situ clean-up verification method used at the end of the completion process when starting production of petroleum fluids while the completion rig is still at the well location. The method comprises the following steps:

- marking one or more of separated zones (SI, S2, S3, ..) along the well by one or more distinct tracers (T10, T20, T30, ..), before starting the production,

- wherein the tracers (T10, T20, T30, ..) are added along with the completion or the clean-up fluid,

- wherein the tracers (T10, T20, T30, ..) are oleophilic, - wherein the tracers (T10, T20, T30, ..) as such are optical detectable,

- wherein the tracers (T10, T20, T30, ..) are arranged for to be released from every each zone to an inflowing fluid of oil or gas,

- starting up the production,

- collecting at least one sample of the produced petroleum fluid,

- processing the sample to change the tracers (T10, T20,

T30, ..) into nonoleophilic (oleophobic) tracers (Tlw, T2W, T3w, ..),

- separate the now non oleophilic tracers (Tlw, T2W, T3w, ..) from the oil (0) in the sample,

- optical inspection of the non oleophilic tracers (Tlw, T2W, T3w, ..), to verify whether, or not, all of the tracers (Tlw, T2W, T3w, .. ) occur in the sample and with that in the

produced petroleum fluids, or not, to verify if inflow of petroleum fluids in the tracer marked separated zones (SI, S2, S3, ..), takes place, or not, in the start-up phase of the production. This is to give a basis to validate if the

petroleum well is satisfactory cleaned up and one then may initiate relocation of the drilling rig.

Embodiments of the invention A verification of the clean-up process may be performed by the use of chemical compounds as for instance substances that may be detected by use of spectroscopic methods as UV, close to IR, Fluorescence, and the like. By the use of systems which leak high concentrations of dyes/tracers it is sufficient with low cost detection equipment that measure concentrations in a typical range 100 ppm - 1 ppb.

A method according to the invention may shortly be described by that for instance different chemical substances/tracers

(e.g. a number of 2 - 4) are placed out in the well by the use of the available completion solutions, and wherein the chemical substances/tracers are spread out from "heel" to "toe" (different zones) . If all the chemical substances may be detected within the clean-up process, one may conclude that the process is good enough, and the rig may be relocated.

Due to the fact that the produced oil contains components that may cause interference (have absorption maxima

themselves) in UV and VIS range, the present invention comprises chemical compounds/substances that during

installation (completion) are oil-soluble (leaking to into oil), but at the rig may be isolated from the oil phase by simple extraction using organic solvents, water based

solutions or combinations thereof, in such a way that the solution will not be miscible with the oil phase, but forms an own phase or transfer into an added phase which is not miscible with the original oil phase (sample) .

A solution to the problems mentioned above is a method for rapid verification of satisfactory clean-up at the end of the completion process when starting production of petroleum fluids while the completion rig is still at the well location comprising the following steps: Firstly, marking one or more of separated zones (SI, S2,

S3,..) along the well by one or more distinct tracers (T10, T20, T30, .. ) , before starting the production.

The tracers (T10, T20, T30, .. ) are added along with the completion or the clean-up fluid. The tracers (T10, T20,

T30,..) are oleophilic. The tracers (T10, T20, T30, .. ) are optical detectable, or becomes so through chemical processes carried out after sampling but before the analysis /the detection takes place. The tracers (T10, T20, T30, .. ) are arranged for to be released from every each zone to an

inflowing fluid of oil or gas. The first starting up of the production is then carried out. One accordingly collects at least one sample of the produced petroleum fluid. The tracers should be released in relatively high concentrations,

prefferably in the range of 1 ppb to 10 ppm.

The sample or samples are then processed to change the tracers (T10, T20, T30, .. ) into non oleophilic (oleophobic) tracers (Tlw, T2W, T3w, ..), preferably into water-soluble tracers. Thereafter the now non oleophilic tracers (Tlw, T2W, T3w, ..) separates from the oil (0) in the sample. An optical

inspection of the non oleophilic tracers (Tlw, T2W, T3w, ..) is then carried out, preferably in the water solution, to verify weather, or not, all of the tracers (Tlw, T2W, T3w, ..) occur in the sample and with that in the produced petroleum fluids, or not. With that one may verify if inflow of

petroleum fluids in the tracer marked separated zones (SI, S2, S3, ..), takes place, or not, in the start-up phase of the production. Thereby one may immediately tell if the petroleum well is satisfactory cleaned and that one may order rig-down and/or removal of the completion rig.

The chemical substances which are desired to be detected have to be of such a nature that they do extract from the oil phase into the above mentioned solvent /water phase under conditions that hinder natural oil components to be extracted into the particular phase in as large a scale as possible.

It is also possible to use water soluble tracers/substances which releases to a water based completion phase, and wherein these thereby easy separates from the presence of potential oil phases. The method for a rapid verification then comprises the following steps:

Firstly, marking one or more of separated zones (SI, S2,

S3, ..) along the well by one or more distinct tracers (Tl, T2, T3, ..), before starting the production.

The tracers (Tl, T2, T3, ..) are added along with the

completion or the clean-up fluid. The tracers (Tl, T2, T3, ..) are optical detectable, or becomes so through chemical

processes carried out after sampling but before the analysis /the detection takes place. The tracers (Tl, T2, T3, ..) are arranged for to be released in relative high concentrations from every each zone to an inflowing fluid of oil or gas. The first starting up of the production is then carried out. Then, one accordingly collects at least one sample of the produced petroleum fluid. It is no need for extraction and the water phase can be analyzed. Thereafter an optical inspection of the tracers (Tl, T2, T3, ..) is carried out, preferably in the water solution, to verify whether, or not, all of the tracers (Tl, T2, T3, ..) occur in the sample and with that in the produced petroleum fluids, or not. With that one may verify if inflow of petroleum fluids in the tracer marked separated zones (SI, S2, S3, ..), takes place, or not, in the start-up phase of the production by use of the inspection method mentioned below where the water soluble tracers (Tlw, T2w, ..) will be identical to the distinct tracers (Tl, T2, ..) mentioned here. The desired characteristics for the tracers according to the invention may be obtained by comprising chemical

substances/compounds which is incorporated in an oil soluble form. This may be performed by chemical compounds comprising acidic functions (carboxylic acid, sulfonic acid or the like) or other functional groups that may be ionized under different conditions (amines etc.), incorporates while they are in a non ionized form (oil soluble) . When they are to be extracted to water or an organic phase, one may manipulate the pH to give charged chemical compounds which, by that, will be transfered to the more polar phase. Detection of the dyes may then be carried out from these mentioned polar phases with little interference from the natural existing oil-soluble components that may cause interference. With other words one may say that during the extraction the tracers, which comprise chemicals, changes from being oil soluble to become water soluble in polar solvents.

In an embodiment of the invention the treatment of the sample comprise a chemical reaction classified as an acid-base equilibrium reaction that introduce water soluble groups in the tracer molecule structure.

In another embodiment of the invention the treatment of the sample comprise a chemical reaction classified as a cleavage reaction which introduces water soluble groups in the tracer molecule structure.

In another embodiment of the invention charged chemical substances with "hydrophobic" counter ions may be used, in a way that the molecules (complexes) overall becomes hydrophobic and thereby oil soluble. For instance in aqueous solutions the counter-ions will be exchanged by added hydrophilic counter- ions in the polar or water based solution through an extraction step. The dyes/tracers will then become soluble in the polar or water based solution.

In another embodiment of the invention one may use tracers which comprise chemical substances which are esterified

(esters of carboxylic acid, sulfonic acid, phosphoric acid) or chemical substances comprising other chemical groups which are chemical modified (protected) by hydrophobic units, and wherein those units will split of under the extraction so as the dyes becomes water soluble or soluble in polar solvents. In an embodiment of the invention the optical inspection by the non oil soluble tracers (Tlw, T2w, T3w, ..) is carried out by a spectral analysis for instance in UV-light or light in the visible light spectrum. Light close to IR may be used as well .

In an embodiment of the invention the detection of the

different tracers will be carried out by the use of

fluorescence, photoluminescence, laser induced fluorescence, or DOE (diffractive optical elements) .

In an embodiment of the invention the separation and detection of the tracers will be carried out by thin layer

chromatography (TLC, Thin Layer Chromatography) with following optical measurements.

In an embodiment of the invention the separation and detection of the tracers will be carried out by chromatography in micro channel flow system and following optical measurements.

Advantageous with TLC and micro channel systems are that they are well suited for optical measurements or inspections.

In an embodiment, if the tracers do not give the requisite response by UV or visible light, aerosol may be used to

"develop" the tracers for to further visualizing by the use of e.g. UV, visible light or close to IR light.

Placement /installation of tracers The tracers being used in the invention may be incorporated in a matrix (high content of tracing material) which is placed as a part of a sand screen or another part of a well completion. Release of the tracers takes place through different events as dissolving of matrix comprising tracers comprising chemical substances/ tracer materials, by swelling of the matrix or by a protection casing/ container comprising tracer, is

perforated or destroyed by the means of controlled incident ( i.e. physical shooting of holes), solvents etc.).

Another possibility is to insert (fill up) highly concentrated solutions of chemical compounds in a cavity that is a part of the mechanical completion. Release of tracers may then be carried out by shooting holes in (perforate) the particular completion zone or to use valves of different types (manual controlled or wireless) .