A large onshore oil field in Saudi Arabia is supported by peripheral water injection that started 40 years ago. Parts of the field are becoming mature with increasing water production. This poses a challenge as well production is declining and/or, in some cases, ceasing to flow as water cut increases, leaving in-place oil potential that needs to be recovered. Increased water production has another side effect of increasing operating cost to handle and recycle unwanted additional produced water. To reduce water production and reactivate the dead wells, several options were implemented, including facilities operational changes, workovers, and rig-less chemical and mechanical techniques.
One of the easiest and most cost-effective techniques that has been used in the field to reduce water production is the application of the rig-less Through-Tubing Bridge Plugs (TTBP). This paper presents 15 years' experience of the application of TTBP in vertical open and cased holes as well as slightly deviated wells. Data were reviewed for more than 130 wells that had water shutoff jobs using TTBP. The paper discusses results and factors, and reservoir as well as completion parameters that contribute to the success of this rig-less water shutoff technique. These factors include permeability thickness and productivity index, well completion, very high permeability intervals, reservoir pressure, tight porosity intervals, and the flowing wellhead pressure. Discussion of the economics of the application is also presented.
Introduction
An onshore oil field, produced initially in 1951, is supported by peripheral water injection that started in 1965. Increased water cut causes well production to decline and/or in some cases cease to flow, resulting in leaving oil unrecovered. Figure-1 shows an actual example of a well's production rate decline due to increased water production. Increased water production also increases the handling operating cost.
Vertical wells in this field cease to flow due to increase in water cut ranging between 30–80% depending on the reservoir characteristics and due to system back pressure. The oil handling facilities in this field were operating at 150 psi and, in an attempt to revive dead wells, some of the facilities had their operating pressure successfully reduced to 120 psi and could not be lowered further. The facilities' gas capacities were limited to handle the increased evolved gas rate. At present, economics does not support expenditures to handle excess gas rate from the oil wells.
Many rig-less technologies are available to shut-off or reduce unwanted water production using cement, marble chips, bridge plugs or polymer gel, etc. One of the easiest and most cost effective techniques being used as a routine method in this field to reduce water production is the application of Through-Tubing Bridge Plugs (TTBP).
Field Description
This onshore oil field is 280 km long and 26 km wide and is supported by peripheral water injection. The pay zone is approximately 250' thick and of carbonate formation with some dolomite sequences. The pay zone is subdivided into 4 zones with the best productivity in Zone-2. Although sweep is irregular in some parts of the field, in general, the sweep is uniform and from bottom up vertically. A normal flow meter profile is shown in Fig. 2. Most wells were drilled vertically penetrating the whole pay zone with 6–1/2" open holes or 4–1/2" perforated cased holes. With the advancement in horizontal drilling technology, the current practice is to complete all producers highly deviated or horizontal with one or multi-laterals.
High permeability streaks, or as called Super-K layers, are common in the field and concentrate mainly in the dolomitic facies. These layers may cause irregular water flood movement especially if they are connected to faults or fractures.