The Volve oilfield has three types of Well completions designed with offshore completions: Oil production Wells, Water injection Wells and Water production Wells. The Wells are deviated and drilled from a single offshore Well-pad.

The Oil Wells have cased hole completions with production tubing and packers. Here we’ll look at the completion of two Oil Wells:

Well 15-9-F-11: Horizontal, Drilled in the first phase of field appraisal
Well 15-9-F-14: Monobore deviated, Drilled in the second phase of field appraisal

Well completion is the process of making a well ready for production (or injection) after drilling operations. This principally involves preparing the bottom of the hole to the required specifications – casing, cementing, running in the production tubing and its associated down hole tools as well as perforating and stimulating as required.

Image 1: Well-wise oil production from Volve oilfield

Well 15-9-F-14

The Well 15/9-F-14 was the second producer of the Volve Field (Blue curve in Image 1) . It is located on the structurally highest point of the Volve structure.

Water Depth/air gap: 91 m MSL/ 54.9 m RT

Completion type: 7″ monobore perforated liner

Casing

The completion design for the oil producer is 5-stage completion design with a 7’’ monobore. The design life of the wells is expected to be 10 years.

Casing / liner Size (inch)	MD Top (m RT)	MD Bottom (m RT)	Remarks
30	140.68	196.8	Set approximately 100 m below mud line for foundation
20	145.68	1077	Set below Skade Fm at 1077 m RT
14	140.68	2275	Set into Ekofisk fm (Shetland)
10.75	21.8	1604	Set above the Roedby formation
9.63	1604	2783	Set into top of Hugin reservoir
7	2616	3685	Set at TD

Perforation

The perforation strategy for F-14 is governed by two main issues:

Obtain enough perforated intervals to reach sufficient PI
Avoid perforating the weaker thief zone which has a sand production potential. The thief zone is referred to as the reservoir zones with permeability exceeding 3000 mD.

To obtain sufficient PI it has been recommended to perforate sufficient length so that a kh-product of about 90,000 mD-metres is obtained. In the base case this requires perforation of 60 m MD in upper reservoir zones (zones 1-5) and the whole interval of 147 m MD in the lower fault block (zones 10-14).

This results in a blank pipe of 200 m MD between the upper and lower perforations which will make it possible for future interventions either to isolate the lower fault block and/or perforate the lower zones of the upper fault block.

The strategy is to deploy the perforation with TCP guns on drill pipe and perforate in overbalance before running the completion string.

Zone	MD Top (m)	MD Bottom (m)	Phasing (Deg)	Shots/ft
Hugin	3005	3020.2	10/350	4
Hugin	3021	3036.2	10/350	4
Hugin	3044	3059.2	10/350	4
Hugin	3287	3296.2	10/350	4
Hugin	3312	3321.2	10/350	4
Hugin	3345	3354.2	10/350	4

Perforations in the Well 15/9-F-14

Gas lift

A gas lift mandrel with a dummy valve will be installed in the well at 1366 m MD. Simulations show that gas lift will not be necessary at first start-up of the well, but can be a necessary aid at later production starts when the water cut has increased. The gas lift can also improve recovery late in field life.

Asphaltene inhibitor injection

The onset of asphaltene flocculation is detected only 10-20 bar below the initial reservoir pressure, so precipitation of asphaltenes in the formation may occur if the draw-down into the well bore is larger than about 20 bars. It has therefore been found necessary to be able to inject asphaltene inhibitor down hole.

The asphaltene will be pumped from the surface through a ¼’’ line down to a valve installed above the production packer.

Pressure and temperature measurements

Down hole gauges providing pressure and temperature measurements will be installed below the chemical injection valve to supply real-time down hole data. These will contribute to increased reservoir understanding and production optimization.

Well interventions

The well is a near monobore completion which makes future interventions easier. Expected interventions are:

Replacing the initial dummy valve with a gas lift valve
Production logging
Water shut-off with straddle pack
Scale squeeze / Well washing

Well 15-9-F-11

Well History

The objective of the well is to identify potential hydrocarbons in two prospect segments immediately Northwest and North of the Volve field. In case of a commercial find the well will be designed to immediately produce from one of the prospect segments.
In case both prospect segments are dry, the well is designed with a fallback option towards an IOR target located between the existing producers F-12 and F-14.

15/9-F-11 / 15/9-F-11 T2 pilot Volve North prospect

Top Hugin Formation was encountered 27 m TVD deeper than expected at 3181 m MSL. The well proved a dry Volve North prospect. A dry North prospect resulted in the cancellation of an immediate 15/9-F-11 B North producer.

15/9-F-11 A pilot Volve Northwest segment

It encountered oil-filled Hugin Formation at 2944 m MSL, thus 25 m TVD deeper than expected. The well proved a thick upside oil column in the NW segment, which is in pressure communication with the main field.

15/9-F-11 B IOR infill

It encountered an oil-filled Upper Hugin in heel and toe with good reservoir qualities similar to offset wells F-12 & F-14. A total of ~760 m MD in gross oil bearing productive Upper Hugin were encountered. Production was started July 24th 2013 with an initial nearly water-free rate of ~1000 Sm3/d.