Drill Stem Testing
A) DST jobs
DST jobs are used to verify the inflow from the reservoir during and after drilling and also for the perforation of the horizon in concern. The result of the pumping test is to obtain the sample of the borehole formation and the pumping pressure record. These results provide important information about the value of the borehole pressure, permeability, skin factor and production of borehole formation.
DST jobs are carried out by the equipment supplied by the Johnstone Company. DST work is either performed in an open hole with the 72 mm to 311 mm diameter casing or in closed hole with the 2 ¾” to 13 3/8” diameter casing.
The interval in concern can be isolated by using two packers in tandem or by the straddle test. The hold-down packers and the supporting packer can be used separately or in an assembly with a hydraulic anchor to perform stimulating jobs or swabbing.
Results of the DST are:
- quantitative and qualitative description of media in the drill stem testing area
- complex course of pressures obtained during the test
- formation pressures
- average conductivity in the incoming area
- skin factor (respectively DR or EDR factors)
- potential productivity
- modern and fast method for testing horizons in oil, gas and water wells
- essential time reduction needed for verification of the flow
- possibility to perform the production test in wells where swabbing is less effective
On the basis of the test interpretation we are able to recommend suitable stimulation work .
B) Mechanical bridges (MB)
The isolation of already depleted horizons or horizons unsuitable for further mining are carried out by mechanical bridges in casing boreholes with 6 5/8” and 7” diameter.
Dimensions of the MB
- total length: 485 mm
- outer diameter of the sealing elements: 136 mm, 146 mm
- pressure drop: 25 MPa
The mechanical bridge is lowered by oil well tubing pipes or drilling pipes. The pressure of 12,6 MPa and mechanically by 7 tone is needed to place the mechanical bridge in the correct position. The bridges are disconnected either by rotating or pulling.
Logging measurements can be used to ensure the absolute accuracy of the setting.
C) Production tests
The F-O-F station equipment is used to carry out the production tests, cleaning of the gas wells and measuring the productivity of the wells in the underground gas storage reservoirs and measuring productivity of the oil fields. The equipment uses a three-phase separator with its own regulator for incoming gas pressure and temperature. It consists of a powerful combustion burner and storage tanks for individual reservoir formations.
This equipment can be used for precise calculations of the reserves in the tested structures over a longer period of time. The station is equipped with its own 3” measuring track with a replaceable shutter, where static, differential pressure and temperature are recorded.
D) Gravel pack operations
Gravel pack equipment (screen and sand) prevents the progress of the free formation material into the production wells. It protects the well completion against plugging up and the abrasion. It is performed especially in the underground gas storage reservoirs but also in crude oil and hydro boreholes. The gravel pack operation is carried out in open hole or in the casing after milling off a part of a string casing. This causes the consequent broadening of the formation in concern to the required diameter. Our company offers full services, that means: projects, stainless steel screens of the required diameter, gravel pack fluids and all equipment needed for the wells’ assembly.
During the gravel pack operations we use the best quality material: stainless steel screens from Backer weld and Excluder 2000. The area around the filter is filled with clean Quartz sand in standard granularity according to API RP 58.