The HTHP test is used mainly with Oil Based Mud although it may be used with water based mud under certain circumstances such as in high temperature wells or wells which exhibit a high risk of differential sticking.
HTHP testing of water based mud is not routine and shall be specified in the Drilling Fluids Programme.
The test is used to determine the static filtration characteristics of the mud and the need for treatment with fluid loss additives under conditions of high temperature and high pressure.
Normal test conditions are 150oF and 500 psi differential pressure.
Maximum allowable test temperature is 300oF with the standard equipment.
The filter cake thickness is measured and must be maintained below 2 mm.
Filtrate collected during HTHP testing must not be used for subsequent chemical analysis.
The HTHP fluid loss must be maintained within the programmed specification to limit potential for differential sticking and formation damage in the reservoir.
Equipment
HTHP Filter Press and heating jacket.
Calculation
In order to compare with the low pressure test, which has a filter area twice the size of the HTHP filter press, the volume of filtrate must always be doubled.
Reporting
|
Parameter |
Unit |
Accuracy |
|
Filtrate Volume (filtrate collected in 30 mins x 2) |
ml |
± 0.1 |
|
Filter Cake Thickness |
mm |
± 1 |
|
Test Temperature |
°F |
± 1 |
Sources of Error
Ensure that the pressure remains constant throughout the 30 minute test period.
Ensure that test is performed at the correct temperature and that the temperature remains constant throughout the test.
Pressure gauges and metal thermometers must be regularly maintained and calibrated.
Replace leaking gaskets and seals.
Ensure cell and measuring cylinder are dry before beginning the test.
Safety Note: Compressed gas is used in this test. Caution must be exercised when disassembling the cell after testing. Adhere strictly to manufacturer’s operating instructions. Ensure correct operation of valves. Clean out any obstruction in the bore.