The invention also relates to an arrangement to be used for the such monitoring.

From US patent specification 5 163 321 (Perales) there is known equipment comprising a pipe having an internal fibre-optical cable or a thermocouple to be used for measuring pressure and temperature in hydrocarbon wells or geothermal wells. The pipe is filled with a medium which is better adapted to the components than is other- wise the fluid in the well. The measurements which are taken are made continuously, and there is no need for electronics or soldering points in the well or in the well head. The pressure is measured on the surface and is thereafter extrapolated down to the desired depth, by estimating the density of the fluid and measuring the hight thereof.

From US patent specification 5 275 038 (Sizer et al.) there is known a system for inspecting wells, whereby is injecte a pair of fluids through a pair of concentric reeled tubings. One of the fluids is acoustically homo- geneous and possibly optically transparent. The lower part of the pipe comprises an optical sensor which can report something about the condition of the well, which is communicated through the transparent fluid.

The second fluid is used for for example cooling down an optical sensor. The use of fibreoptic cable in connection

with such an optical sensor is, according to this publi- cation, presented as an alternative solution.

US patent publication 5 419 188 (Rademaker et al.) relates to modular telemetry link which can be used in connection with what has been disclosed in said US patent publication 5 275 038. The modular telemetry link is located in the lower part of a coiled tube and can receive signals from various types of sensors. This pub- lication does not disclose the use of downhole telemetry link generally, the importance of the link being related to its use for inspection. Further, the link is used in connection with a method which entails injection of an optically transparent or acoustically homogeneous fluid.

GB-2 284 625-A relates to a structure comprising a rod or a pipe made of composite material, which along its longi- tudinal axis is provided with sensors for measuring pres- sure, temperature and/or conductivity. A telemetry link is used to control the signals and the transport thereof to a platform.

NO patent publication 173.069 discloses a system for acquiring data and a sampling method which reduces the energy consumption and necessary storage capacity to a minimum. This can be done for a plurality of unequal sensors in relation to a customer's requirements and site conditions.

From US patent publication 4 763 259 (Delatorre et al.) there is known a self-contained downhole tool for logging pressure and temperature. The tool can, on the surface, be diagnosed from the outside without any demounting.

Thus, the prior art technique presents a general measur- ing of pressure, temperature and depth or fluid level in drilling holes and wells, but without giving any instruc- tions for how such measuring tools can be located in a

current reservoir for acquiring further relevant data relating to a specific reservoir.

Disclosure of the invention The object of the present invention is to provide a method and an arrangement which to a larger degree uti- lizes the possibilities of acquiring relevant data in connection with a reservoir, specifically during test- production and/or production operation of the reservoir in question.

Consequently, the present invention gives instructions for a method as stated in the preamble, which is charac- terized in that for said monitoring there is used infor- mation relating to such parameters also from non-produc- ing wells in the reservoir field.

Further, the invention gives instructions for an arrange- ment which is characterized in that in non-producing wells in the reservoir field there are provided means for reading parameters in said wells, which are related to the monitoring of the reservoir in question.

Further features and advantages in connection with the present invention will appear from the following descrip- tion taken in connection with the appended drawing.

Brief discussion of the drawinq Fig. 1 is a schematic layout of an arrangement or a sys- tem according to the present invention, wherein the method according to the invention can be applied.

Description of embodiments The object of the present invention is to monitor pres-

sure, temperature, hight of fluid and gas level, etc., in wells which are distributed in an area, for thereby ob- serving whether these parameters are influenced by pro- duction and/or injection from and/or to one or more wells at a distance therefrom. Preferably, such monitoring equipment should be used for example in a prospect well without completion pipe, respectively in any non-produc- ing well in the current reservoir field.

One embodiment of the invention may therefore involve that one or more sensors are suspended in a prospect well, whereafter said well is plugged and cemented. One should then prepare penetrators of, for example, glass- metal-type for thereby meeting the requirement of neces- sary number of barriers towards said reservoir. In con- nection with a well head the present method and arrange- ment may comprise a control module which acquires data for further transmission thereof or storing thereof for later retrieval.

In Fig. 1 there is schematically illustrated a view which explains one embodiment of the invention, there being indicated in Fig. 1 a reservoir field 1, comprising a main well 2 which is used for test production and/or production operation, which test production and/or pro- duction operation will influence the parameters which are of interest in the reservoir field 1, for example pres- sure, temperature, hight of the water and gas level, etc., not only in the vicinity of the main well but in the overall area comprised by the reservoir.

The main well 2 which is located at the sea bed 3, is via an appropriate riser pipe and an umbilical connected to a test or production vessel 5 which is on the surface 6 of a body of water 7, and which according to the invention is adapted to receive further information about the re- servoir 1, not only from its own drilling hole, but also

information related to such parameters from non-producing wells, for example a well as indicated by reference numeral 8. This can generally be a non-producing well, for example a prospect well, or a slim hole well, which has been plugged after the drilling.

In other words, the invention gives instructions for a method and an arrangement wherein are used measuring parameters from wells, for example well 8, which are completely or temporarily out of production, comprising for example rejected conventional test wells or slim hole wells, respectively wells which are only partly prepared for possible production.

Further, according to the invention there are given in- structions for taking into use parameter information from for example wells without a valve tree, wells with or without production pipe, wells without any connected completion or well maintenance vessel, etc.

It is to be understood that most appropriately there may be used measuring signals coming from parameters at the bottom side of one or more barriers in the current well 8, which barriers must adhere to the requirements accord- ing to related laws, and specifically parameters which then are read without any oil flowing to the surface.

It is to be understood that preferably there may be used measuring signals coming from parameters at level with the reservoir, as this is indicated at the well 8 in Fig.

1.

Further, it is appropriate for communication of parameter information to use a module 9 at the well head 10, which module may communicate with instruments down in the well 8 and further communicate said information to the user, more specifically the production vessel 5, or similar.

In an appropriate embodiment of such a module 9 this may be adapted to process, for example compress the data being received from said instruments, such that said data can be transferred via an appropriate transmitter 11 in the area of the well head 10 to a receiver station, for example the mentioned production vessel 5, or a produc- tion platform, especially via a telemetry link, which is illustrated by reference numeral 12, which possibly involves moderate requirements as regards capacity.

Cables for transmitting power and signals may be used if appropriate.

For the communication of well parameters which are sensed and processed in a plugged well, for example the well 8, there may be used instruments which are located down in the well 13 before the plugging of the well, possibly self-contained instruments or instruments which via one or more static barriers 14 are connected with said module 9 by means of appropriate electrical and/or optical cables.

For operating the instruments providing the desired re- servoir parameters at the plugged well 8, there may ap- propriately be used a sea water battery.

During operation of the reservoir the parameters of the plugged wells or so-called"slim hole wells"may be read at given intervals, possibly upon request from a remote control station, for example from said production vessel 5, an underwater production station, or similar.

Preferably, the instruments which are used for sensing the related parameters, may be specifically located in the area of the so-called"reservoir"interface of said well, and more specifically for sensing pressure P, tem- perature T, and specifically for measuring the hight of oil/water-How and oil/gas-contact Hgo.

The instruments to be used for sensing the related para- meters may appropriately be located along for example a coiled tube string, which string can be attached to the profile of the well head 10, and possibly comprising a pressure barrier for electrical and/or fibreoptic wires.

It may be appropriate that in one or more of the non- producing wells 8 there is used a unity connection which in turn may be utilized by for example a remotely ope- rated vehicle upon connection and analysing of the ins- truments and the control means, possibly for reprogramming said control means and/or modules.

Due to safety reasons there may at the non-producing wells also be used a detector for possible hydrocarbon leakage from the respective non-producing well.

Further variants of the present invention may involve: 1) to include seismic sensors down in the well, as well as transferring the communication link from the produc- tion vessel to the seismic vessel for a shorter period, possibly communicating with both, 2) to use radioactive or chemical analysis instruments down in the well, such as to measure the concentration of trace materials in the reservoir fluid which may flow transversely through the well, 3) the communication between the module at the well head and said instruments may take place acoustically through flow pipes or casings in the well. The power to the instruments may then, as an example, be supplied from a number of thermocouples which are arranged vertically in the well between two temperature potentials (this can be done because there is no flow upwards from the well).

If the (geometrical) upper"soldering point"of the

thermocouple is on the bottom side of the arrangement plugging said well, penetrations for instrument power and communication are avoided, 4) to replace the sea water battery with thermocouples in order to supply power to the well head module. In this utilization penetrators are not avoided.