DST tools we use include 3 sorts: APR, MFE and Inflatable.
DST string can be run in hole with TCP equipment in one trip.

APR tools
Annulus Pressure Responsive (APR) tools, used for cased-hole test, are safe, fast and reliable, with unlimited flow and shut-in cycles, and full bore tools. Testing wellbore size is from 4-1/2" to 9-5/8".
This test string is used for cased-hole test and can run in a hole for a relative long duration flow test. It is composed of a multiple circulating valve (OMNI valve), test valve (LPR-N valve), retrievable packer (RTTS packer), gauge carriers and so on. These tools can undertake 15,000 psi pressure and be H2S sustainable. The minimum full-bore size is 2.25" ID for 5" APR tools and 1.8" ID for 3-7/8" APR tools.
This string is operated by annulus pressure. It is safer, faster and more reliable than ever. APR testing string can test one target formation without any un-plugged perforated intervals under the test interval with one packer, or any selected formation with two packers. Other smaller gauges or tools can run through them for perforating, pressure testing, PVT sampling, acidizing and fracturing, etc. This tool string can test several intervals one by one in a single trip. In high volume wells, the full opening features permit flow rates high enough to obtain more definitive test data, so test results are more reliable.

MFE Tools
The Multi-Flow Evaluator system (MFE) is a general name given to a down hole valve that is operated by test string reciprocation up and down, using a part of the string weight to open. The valve has three sections: the valve and sampler, the hydraulic delay and the index system. While running in the hole, the valve is in the closed position and the tool is fully extended; if the packer hits a bridge or restriction, the valve tends to cycle into the open position.
There are 2 sizes of the MFE tool: 3-3/4" and 5".
The MFE tool can be used for open hole off-bottom testing, inflate testing as well as cased hole testing.
The MFE tool string consists of Pump-Out or/and Plug Reverse Tool, Multiflow Evaluator Valve, TR Hydraulic Jars, Safety Joint, Safety Seal, Packer, Pressure Recorder Carrier and so forth.

Inflatable tools
Principle
Inflatable tools are used in longer open holes. During testing, when the tool is running in the hole at the determined depth, rotating the drill-string, the inflatable pump will squeeze drilling fluid to the inflatable packer, and then the packer gets inflated and sets at the well bore, provides a seal and isolates formation and annulus. Through controlling the downhole hydraulic shut-in tool to open and shut-in the well, the gauges will record pressure and temperature data.

Feature and Advantage
Before running the production casing, we use these types of tools to pretest the target zone. We can determine whether the formation is valuable or not, then run the casing, or cancel the casing plan to save money. This type of testing can be used to discover reservoirs and get more reliable information in time.

String Structure
The tool string is mainly composed of a drill-stem or tubing string, hydraulic shut-in tool, inflation pump, inflatable packer, gauge carriers and hydraulic jar. An inflatable packer is usually used to reduce the risk of getting stuck by a long tailpipe supporting in off-bottom testing and increase safety and reliability in open hole testing. Of course the open hole test still has more risk than the cased hole test so there is a need to plan carefully and limit flowing duration time.
Using two packers in an inflatable testing string lets us perform a straddle test to test any formation.

NAVI pump
A NAVI Pump is used to pump the reservoir fluid out, by installing it in the DST string, with the drill rig or workover rig when formation fluid can not flow to the surface due to the pressure being low for testing production rates and liquid properties.

Features and Benefits:
Driven by the Rotary Table and Drill String
High pump efficiency
No gas lock
The output is proportional to the rotation speed
Nominal Net Head is 400 m. Max. Net Head can reach 800 m.
Apply to the low pressure & high flow rate formation