Cuttings injection system is used to inject particles into the mud system before test section stream flow. Two control valves as shown in Figure 1 were used to separate the injection system from main flow line.
The function of the two control valves was to divert the flow of the drilling mud into the flow line where drilled cuttings were injected. These control valves were opened once the experiment was initiated, after the desired flow rate was steadily achieved.
Valves were arranged to ensure smooth injection of cuttings into the system and placement of cuttings in front of the flow stream. Valve arrangement permits isolation and connection of cuttings trap from the circulation system and diverts of the flow stream behind the injected cuttings.
Before the cuttings are injected, they are prepared according to the size and density. To get the more accurate picture of simulated field cuttings value, three phase cuttings were used in this experiment. This can be categorized to small, medium and large.
Preparation of drilling mud
Prior to the simulated hole cleaning, conventional water-based mud (WBM) and water-based mud containing nanosilica (n-WBM) were prepared to determine their rheological properties for cuttings transport application according to API standard for WBM (API RP 13B-1, 2009). 0.15 g caustic soda was introduced in 350 ml fresh water and mixed thoroughly for 4 minutes with 20N IKA Rw mixer. 25 g potassium chloride (KCl) was introduced into the solution and for 6 minutes.
Thereafter, 15 g bentonite was introduced into the solution and mixed for 5 minutes. 1.5 g polyanionic cellulose (PAC) was introduced into the solution and mixed for 5 minutes. 0. 25 g soda ash was added into the solution and mixed for 5 minutes. Later, 195 g barite introduced into the solution was mixed for 30 minutes as contained in Table 1.
Finally, a 1:1 of SiO2 nanoparticle was added into 50 ml reagent bottle containing 30 ml fresh water at different concentrations and sonicated for additional 25 minutes. The pH of the solutions was attuned and sustained at 8.5 – 9.0, and the mud density was maintained at 10 ppg. The mud tank used in the study is illustrated Figure 2.
The mud tank has a capacity of 190 litres with dimension of 24″ diameter and 26″ height. A stirrer was installed to ensure proper mud mixing. The stirrer was driven by 0.25 hp (0.18 kW) electric motor of 1350 rpm. The tank was opened from above and equipped with a calibrating container. A plastic sieve with size of 0.8 mm was used to sieve the cuttings from the return mud.
API and HPHT filtrates loss
The determination of API filtrate loss volume was measured at 100 psi and at room temperature for 30 minutes. The filtrate loss volumes were taken for each sample at every 5 minutes and the filter cake thickness was estimated. The HPHT filtration properties at 500 psi differential pressure (100 psi backpressure and 600 psi-controlled pressure) and 250 °F were estimated by HPHT filter press.
The filtrate loss volume was taken at a fixed time interval and the test was terminated after 30 minutes. The deposited filter cake on the filter paper was then carefully sieved and measured.
Effect of flow rate on cuttings transport
The experiment was conducted by using three different flow rates: 0.4 L/s, 0.6 L/s and 1.0 L/s respectively to develop laminar, transition and nearly turbulent flow. As shown in Figure 3, the higher flow rate will increase cuttings transport due to the turbulent eddies. Cuttings transport increases with the increase of the annular fluid flow; turbulent flow has more impact on cuttings transport than laminar flow as shown in Figure 3. Thus, a higher flow rate resulted in a greater cuttings transport.