Return Permeability Test Apparatus NEWRPTA-10k

Coretest · technical description

Return Permeability Test Apparatus · NEWRPTA-10k · CTS-RPTA10K-TD-01 · Rev. A · September 2026

1. Purpose

The NEWRPTA-10k measures how much permeability a reservoir rock sample loses after contact with a drilling or completion fluid, and how much of it comes back when the well is put on production. The sample sits in a core holder whose wellbore-side end plug carries a flow slot. Mud circulates through that slot across the core face under overbalance, at reservoir pressure and temperature, and builds a filter cake the way it does on the wall of the hole. Permeability to reservoir fluid is measured before the mud goes on and again after it comes off, in the production direction, without opening the core holder in between.

The instrument is built for laboratories that screen drilling fluids, additives and lost-circulation material against reservoir rock: mud selection for a specific pay zone, formation-damage studies, acceptance testing of mud systems supplied to a field. One core holder carries the sample through initial permeability, dynamic filtration, return permeability and flow-back.

Rating of the reference configuration: 6,000 psi mud and pore pressure, 7,500 psi confining pressure, 350 °F (177 °C). Wetted parts are 316 stainless steel. There is no ionising radiation source anywhere in the instrument.

2. Method

2.1 Test sequence

A return permeability test runs in four stages, all inside the same core holder and without breaking any connection.

• Initial permeability, K_i. The saturated core is brought to test temperature under confining pressure and back pressure. Reservoir brine, oil or kerosene is displaced from a piston vessel through the core in the production direction, from the far face toward the slotted face, at constant rate. K_i follows from the stabilised differential pressure by Darcy's law.
• Dynamic filtration. Flow through the core stops. Mud circulates from the mud reservoir through the slot across the slotted face at a set rate, with mud pressure held above pore pressure by the chosen overbalance. Filtrate passes through the core, leaves at the far face through the back-pressure regulator and is weighed. Filtrate volume against time comes from the mass record. Circulation continues for the planned exposure time, typically several hours, and may be followed by a static period with the pump stopped.
• Return permeability, K_r. Circulation stops and the mud loop is isolated. Reservoir fluid is displaced again in the production direction at the rate used for K_i. Differential pressure is tracked until permeability stabilises at K_r.
• Result. Return permeability is reported as 100 × K_r/K_i, together with filtrate volume against time and the full record of pressures, temperatures and rates.

2.2 Slot geometry and cake formation

The slot in the wellbore-side end plug is 0.25 in deep and 1.125 in wide. Mud enters through a ¾ in NPT port, sweeps across the face of the core and leaves through the opposite port, so the cake forms under shear rather than by static settling. Shear at the face follows from the circulation rate and the slot cross-section; the rate is an operator set-point and a project input. A face spacer, fitted per project, opens the mud path to the full diameter of the core. Pore-side connections are 1/8 in NPT lines and are kept apart from the mud path, so solids never reach the permeability lines, the differential-pressure transducers or the back-pressure regulator.

2.3 Direction of flow

The two faces are named A, the far face on the reservoir side, and B, the slotted face on the wellbore side. Production is A to B. Mud filtrate invades B to A. The direction manifold routes any of the three vessels to either face and returns the outlet to the back-pressure regulator, so saturation, injection toward the formation, production toward the wellbore and filtrate collection are set by valve position, not by re-plumbing.

3. Construction

The instrument is a floor-standing frame. The forced-air bath holds everything that has to be at test temperature: the core holder, the three fluid vessels, the mud reservoir and the heated tubing. Pumps, regulators, balance and electronics are mounted outside the bath at room temperature. Main units:

• forced-air bath to 350 °F with digital controller and an independent over-temperature trip; two temperature controllers for the core holder and the fluid lines;
• dynamic-filtration core holder, Hassler type, for 1.0 in and 1.5 in samples up to 6 in long, with the slotted end plug, FKM sleeves and spacer set; confining 7,500 psi, pore and mud 6,000 psi;
• three piston-separated fluid vessels, 1,000 cc each, 6,000 psi, 316 stainless steel, for reservoir brine, oil or kerosene, and a reserve fluid. Hydraulic fluid drives the pistons from below, so the transfer pump never touches the test fluid;
• mud circulation module: 1,000 cc mud reservoir rated 6,000 psi at 350 °F, a circulation pump with a solids-tolerant wetted path, a loop back-pressure regulator, and a flush and drain line. Loop pressure is imposed from the reservoir side and set independently of the circulation rate;
• transfer pump, dual-cylinder, constant rate or constant pressure, 10,000 psi rated, driving the vessel pistons;
• confining module, syringe pump in closed-loop pressure control, 10,000 psi rated, 7,500 psi duty;
• direction manifold with vessel selection valves;
• two back-pressure regulators on the flow lines, plus the loop regulator in the mud module; electronic balance with a sealed receiver;
• two absolute pressure transducers, 0 to 7,500 psi, ±0.05 % of full scale; three differential transducers, 0 to 25, 0 to 100 and 0 to 500 psid, ±0.2 % of full scale, selected to suit the permeability of the sample; temperature measurement 0 to 350 °F;
• pressure relief devices per the project P&ID; emergency stop.

Wetted materials are 316 stainless steel; sleeves and seals are FKM rated for 350 °F.

4. Automation and software

The acquisition and control program logs every channel: pressures, differential pressure, temperatures, transfer-pump rate and cumulative volume, confining pressure and balance mass. From these it computes K_i, K_r, 100 × K_r/K_i and filtrate volume against time. Set-points for confining pressure, bath temperature and pump rate are entered from the screen.

Alarm limits on every pressure and temperature stop the pumps. The bath over-temperature trip is a separate hardware loop and does not depend on the PC. Results export to spreadsheet, and the raw record is kept so a test can be re-reduced later without repeating it. The program runs on the Windows PC supplied with the instrument.

5. Engineered per project

The pressure boundary and the core holder are standard. What Coretest selects for each order is the mud circulation pump, the face spacer and the transducer ranges. To size these we need:

• mud type, maximum density and the largest particle size of any lost-circulation material;
• required circulation rate or face velocity across the slot;
• overbalance and back pressure for the filtration stage;
• permeability range of the samples and the flow rates planned for K_i and K_r;
• site power supply and the gases available in the laboratory.

6. Installation and service

The instrument needs a level floor, the power supply listed above, instrument air and a regulated nitrogen supply. Installation and commissioning are carried out on site by a manufacturer's engineer and closed with a commissioning report after a test run on a customer sample. Operator and maintenance training is delivered on site, with a training certificate and an attendance record. A schedule of preventive maintenance and a spare parts and consumables list are handed over with the instrument.

This document defines the product family. Guaranteed performance, included hardware, exclusions, interfaces and acceptance criteria are stated only in the project-specific technical proposal and approved datasheet.

NEWRPTA-10k · CTS-RPTA10K-TD-01 · Rev. A · September 2026 · reference configuration to a 6,000 psi / 350 °F specification

1. Technical characteristics

Figures apply to the reference configuration built to a 6,000 psi / 350 °F specification. Guaranteed values for a project are stated in the project datasheet.

1.1 Operating envelope

1.2 Core holder and samples

1.3 Fluid handling

1.4 Measurement

1.5 Construction and utilities

2. Scope of supply

Guaranteed performance, included hardware, exclusions, interfaces and acceptance criteria are stated only in the project-specific technical proposal and approved datasheet.

Documents for the NEWRPTA-10k Return Permeability Test Apparatus. Guaranteed performance, included hardware, exclusions, interfaces and acceptance criteria are stated only in the project-specific technical proposal and approved datasheet.

• Reference datasheet, NEWRPTA-10k (PDF)
  CTS-RPTA10K-TD-01, Rev. B, September 2026, 11 pages, 728 KB
• Functional flow schematic CT-DF-PFD-001, sheet 1 (PNG)
  Rev. C, functional design, 1800 x 1125 px, 206 KB