Application of Successful New Downhole Fluid Sampling Technique in Ultra Low Permeability Reservoir in Abu Dhabi Onshore

Downhole reservoir fluids sampling in tight formations has been a continuous challenge due to various reasons. The paper presents a technique of successfully collecting downhole fluid samples for first time in ultra-low permeability reservoir having a history of deep invasion. This became possible by initiating micro-scale fractures followed by pumping out for sampling. Using this technique, downhole formation fluid samples were collected, clean-up time was optimized, in addition to acquiring in-situ stress information during the process. A preliminary assessment was performed using open hole formation evaluation logs and pore pressure measurements to identify the most suitable zones for stress measurement and fluid sampling. Single packer sleeve fracture initiation tests were performed to break down the high stress dense layers. In the reservoir rock, the stress measurement involving initiation of a micro-scale fracture was followed by pumping out formation fluid from the fractured zones to collect clean formation fluid samples. The formation breakdown and fracture closure pressure were measured successfully to calibrate minimum and maximum lateral tectonic strains which were valuable inputs for designing the hydraulic fracturing treatment. In the offset wells, fluid sampling attempts from this zone of interest have proven unsuccessful after multiple attempts involving pumping out over 300 liters because of the high depth of invasion leading to a thick flushed zone around the wellbore. The process of initiating micro-scale fractures followed by pumping out provided a high permeability flow channel for efficient fluid sampling. The near wellbore fractures resulted in pumping at higher rates and reaching the higher oil saturated zones of this deeply invaded formation. Hence, formation fluid samples were successfully collected in spite of the low permeability and high invasion typically encountered in this reservoir. Unlike the unsuccessful sampling attempts in the offset wells, this technique of initiating micro-scale fractures in the reservoir rock followed by pumping out helped in collecting formation fluid samples. This technique can be used to collect reservoir fluid samples from micro-Darcy formations and unconventional reservoirs by improving the flow through the induced fractures and thereby reducing the uncertainty that may persist in failing to collect samples from such zones.

Lessons Learnt from a Successful Sampling While Drilling Campaign Delivering Formation Oil Samples and Saturation Pressure Measurements in High H2S Carbonates

As island development strategies gain focus for capitalizing deep offshore assets, limitations like fixed slot location bring about the need for drilling extended reach (ERD) wells with multiple drain holes and complex well geometry to maximize the reservoir coverage for increased production. Pressure testing and reservoir fluid sampling operations require long stationary time and pose a risk of differential sticking. Deploying a pressure testing and fluid sampling tool into the drilling bottom-hole assembly (BHA) helps in maintaining well control through continuous circulation and providing measures to retrieve the tool by rotation and jarring in case of pipe sticking. This paper presents the successful deployment of sampling while drilling tools in three ERD wells drilled using water based and oil based muds to acquire representative formation oil samples from a high H2S carbonate reservoir. The formation oil samples were collected immediately after drilling the well to the target depth for limiting the invasion to collect clean samples in shorter pump-out volume and time. After securing the samples, a phase separation test was performed by fluid expansion in a closed chamber to measure the saturation pressure of the oil. A 30-min long pressure build up was also performed for pressure transient analysis to estimate permeability. Formation fluid samples were collected, while pulling out the drilling BHA, within 12-48 hours of drilling the well by pumping out 100-170 liters of fluid from the formation in 4-6 hours. During clean up, absorbance spectroscopy identifies the fluid phases – gas, oil and water. Prominent trends observed in compressibility, mobility, sound slowness and refractive index measurements add confidence to the fluid identification and provide accurate contamination measurements. Single-phase tanks charged with nitrogen were used to assure quality samples for PVT analysis. The sample tanks are made of MP35N alloy and the flow lines are made of titanium that are both H2S resistant and non-scavenging materials and hence, a separate coat of non-scavenging material was not required. In highly deviated wells, sampling while drilling technology can close the gaps of the conventional wireline operation on pipe conveyed logging in addition to saving 5-days of rig time by eliminating the need for conditioning trips, a dedicated run for pressure testing and sampling and minimizing the risk of stuck pipe and well control incidents The results from downhole fluid analysis and PVT lab are compared in this paper. Going forward, this technology can eliminate the requirement of a pilot hole for pressure testing & sampling by enabling sampling in complex well geometries in landing sections and ERD wells. The paper concludes with discussions on suggested improvements in the tool design and capability and recommendations on best practices to align with the lessons learnt in this sampling while drilling campaign.

Overcoming Downhole Fluid Sampling Challenge Using Dual-Port Straddle Packer in Shallow Viscous Reservoir

Objectives/Scope: Downhole fluid sampling of high quality, low contaminated oil samples with a pumpout wireline formation tester (PWFT) in a shallow unconsolidated reservoir with high H2S, high water salinity and filled with viscous oil is a quite challenging operation. Key properties, related to fluid flow in low pressure reservoirs: formation mechanical weakness, drilling invasion and the high contrast on fluid mobility, have resulted in the failure or impracticality of conventional methods for efficient sampling, resulting in a long sampling time causing high rig cost overhead and often highly contaminated oil samples. Most common problems faced during sampling are: Sand production- causing caving and lost seals and no pressure or samples. Sand plugging of the tool flowline. Operation limitation of pressure drawdown- dictated by extremely low formation pressure and mainly due to having saturated pressure around 20 to 30 psia below formation initial pressure (based on 118 bubble point samples measured in the laboratory). To maintain rock stability and low pressure draw down, fluids were pumped at a low rate, resulting in a long operation time, where a single sample take up to 15 – 20 hours of a pump out. Even with the long pumpout time the collected sample is often highly contaminated based on laboratory PVT analysis report. Methods, Procedures, Process Understanding of the formation properties and its rock mechanics helps to design proper operating techniques to overcome the challenge of viscous oil sampling in unconsolidated sand reservoir. A pre-job geomeechanical study of unconfined sand with very low compressive strength, restricted the flow rate to a maximum drawdown per square inch to maintain rock stability while pumping out. Dual-Port Straddle Packer (figure 1) sampling was introduced to overcome the mentioned challenges. Its large flow area (>1000 in² in 8 ½″ OH section) allowed a high total pumping rate while maintaining very low flow rate per square inch at the sand face, which resulted in an ultra-low draw-down flowing pressure to prevent sand collapse and producing below bubble point pressure that could invalidate further PVT studies. Packer inflation pressure has also been limited to a maximum of 150 to 200 psia above hydrostatic pressure to achieve isolation without overcoming the sand weak compressive strength. During the clean-out operation crude oil tend to separate from water based mud (WBM) filtrate in the packed-off interval due to fluid density difference and immiscibility of the two liquids due to the lower shear rate applied (among others). So a water/oil interface forms within the packed-off interval. As pumping continues, this oil/water fluid contact moves toward the bottom inlet port allowing more clean oil to accumulate at the top. Results, Observations, Conclusions: With the advantage of the dual inlet port straddle packer and the independent opening/closing operating design of each port, a clean segregated oil sample was collected from the top port at an early stage of job operation, saving rig time and cost without compromising collected fluids quality that is valid for PVT studies. Novel/Additive Information: Dual-port Straddle Packer with large flow area (plus filters) with ultra-low drawdown pressure to stay above bubble point pressure in shallow heavy oil reservoirs resulted to be another provided a cost effective technology that can be utilized for collecting downhole samples (DHS) that will undergo PVT studies.

Integration of Advanced Logging Evaluation Techniques Proves Additional Reserves from Thin Bed, Low Resistivity Pay Formations

The biggest clastic reservoir based in Kuwait has been facing evaluation challenges over the thick intervals of highly laminated thin hydrocarbon layers. Conventional wireline tools have a limitation on resolution when it comes to addressing these thin beds. Therefore, the reserves are usually underestimated, and thin pays are often overlooked. This paper presents the integration of a variety of advanced Wireline tools in order to correctly evaluate and compute reserves from these thin pay zones. Acquisition of the triaxial induction tool enabled the study of resistivity anisotropy and the identification of thin pay zones through the distinct reading of the resistivity of the thin sand reservoir. The thin layers have also been further validated using high resolution advanced thin bed analysis from image logs. Advanced spectroscopy and NMR data were used to quantitively define the sand and shale fractions within the thin beds. These measurements were critical to input to improve the resistivity interpretation followed by a reliable estimate of the saturation. High resolution dielectric measurements provided resistivity-independent saturation information enhancing the NMR interpretation using water-filled porosity which was a key input into the identification of the heavy oil presence in Burgan. The newly identified thin pay zones have been further validated using the fluid sampling confirming presence of hydrocarbons with greater understanding of its properties and uniquely quantifying the mobile fluid fractions. The additional available reserves can only be properly determined by combining data from multiple sources to achieve a comprehensive evaluation. Resistivity anisotropy was observed based on the separation of vertical and horizontal resistivities and was therefore investigated to understand its root-cause over different zones. By integrating the results from the dielectric dispersion measurements, the diffusion-based NMR data, spectroscopy data, borehole image interpretation and high-resolution sand count delineation of different lithologic units at a finer scale, we were able to identify thin bedded sand-shale intervals in addition to pin-pointing the heavy oil intervals. Hydrocarbon saturations of individual sand layers showed improvement in hydrocarbon volumes, improvement in permeabilities across the studied zones and increased net pay estimations by 12%. Results from the fluid sampling performed across the newly identified thin pays have validated the advanced logging interpretation results and the presence of hydrocarbons. These intervals were overlooked by the standard basic evaluation and the reservoir potential has been revisited following the latest integrated advanced results. By combining the results of all these advanced wireline answer products, we were able to properly identify and quantify the additional available reserves and therefore change the classification of these reservoirs from poor to excellent with new development plan in place. The paper demonstrates the value solution of the high vertical resolutions taking advantage of the latest advanced technologies to enhance the characterization of laminated thin beds. The integrated advanced solution has enabled improved reservoir potential by the identification of new pay zones initially overlooked by the standard basic measurements.

413 The Clinical Efficacy of Intra-Operative Peritoneal Fluid Sampling in Abdominal infections

Aim To uncover the practical efficacy of intra-operative peritoneal fluid sampling and the impact on antibiotic prescription and clinical outcomes in patients undergoing emergency surgery due to intra-abdominal infections. Method Our retrospective study included all patients undergoing emergency surgery for intra-abdominal infections at Southend University Hospital over 6 months (January – July 2019). Data was collected from electronic patient records, case notes and microbiology reports and included the following information: patient age demographics; type of infection; peritoneal fluid sampling indication; samples taken; details of swab culture report including organisms grown and antibiotic sensitivity; clinical course and incidence of subsequent intra-abdominal infection to include readmission and/or further procedures; the type, duration and route of antibiotic prescribed and duration of hospital stay. This audit was approved by the Departmental Audit Lead. Results 441 patients undergoing emergency surgery for intra-abdominal infection were identified. After exclusions, intra-operative peritoneal fluid samples were indicated in 77 patients (mean age 39.4 years). Of these only 3 had samples taken (3.9%). The most common organisms isolated were mixed anaerobes followed by Streptococcus angiosus. The most common antibiotic sensitivity was Metronidazole and Penicillin. One readmission occurred due to an intra-abdominal tubo-ovarian abscess. Conclusions The study shows that the current practice in our hospital regarding intra-operative peritoneal fluid sampling in intra-abdominal infections reflects the present widely held attitudes regarding its reduced practical utility. Abandoning routine sampling had no significant impact on the clinical course and may be more cost-effective. The study may help surgeons reflect on changing perspectives on this traditional practice.

Unpiggable Pipelines Integrity Assessment by Internal Corrosion Modelling bnd Prediction Based on Topside Piping Inspection Data in The Mature Field Offshore North West Java

Pertamina Hulu Energi - Offshore North West Java, also known as PHE ONWJ, owns 426 subsea pipelines from which only 185 are active operating to support the PHE ONWJ’s production activity and the remaining 241 pipelines are inactive which their status is either remain idle or being preserved. Noted that 67% or 284 of the pipelines aged more than its design life. Onehundred twenty pipelines are still actively operating distributing fluids such as Oil, Gas and 3-phase. Based on the observation, more than 90% of leak events occurred by internal corrosion, that causedby the corrosive agents such high CO2 content, sands or solid particles, SRB and water. The existing integrity management plan such as in-line inspection, fluid sampling, chemical injection and others were performed onto several pipelines. However, PHE ONWJ’s pipeline network facility on Figure 1-2 that is complex and massive, for that reason is not economically to perform in-line inspection to all pipelines. Considering to the conditions mentioned, an effective and efficient pipeline integrity management is developed based on corrosion rate prediction from topside piping within pipeline corrosion circuit as per API 571. This model is constructed from the combination of several parameters like fluid sampling, In-Line Inspection of several pipelines with different services, Topside piping inspection data, Operating history and Design data. The internal corrosion model is developed continuously to validate and used to assess data obtained from In-Line Inspection (ILI) that performed into several pipelines. Since the model is developed, the accuracy ranging 80-99% is achieved. The model is used to predict the maximum internal corrosion rate of PHE ONWJ’s pipeline and become a basis in determining pipeline’s integrity status, remaining life and assisted in assessing the pipeline risk. Those outcome are then become an action plan. Therefore, a joint study is made to create such corrosion model for pipelines. The goal is to have an in-depth approach in managing matured and unpigable pipeline integrity that can be effectively operated gobally and to ensure all stakeholders that it is safe to operate the pipeline.

Feasibility and acceptability of SARS-CoV-2 testing and surveillance in primary school children in England: Prospective, cross-sectional study

Background The reopening of schools during the COVID-19 pandemic has raised concerns about widespread infection and transmission of SARS-CoV-2 in educational settings. In June 2020, Public Health England (PHE) initiated prospective national surveillance of SARS-CoV-2 in primary schools across England (sKIDs). We used this opportunity to assess the feasibility and agreeability of large-scale surveillance and testing for SARS-CoV-2 infections in school among staff, parents and students. Methods Staff and students in 131 primary schools were asked to complete a questionnaire at recruitment and provide weekly nasal swabs for SARS-CoV-2 RT-PCR testing (n = 86) or swabs with blood samples for antibody testing (n = 45) at the beginning and end the summer half-term. In six blood sampling schools, students were asked to complete a pictorial questionnaire before and after their investigations. Results In total, 135 children aged 4–7 years (n = 40) or 8–11 years (n = 95) completed the pictorial questionnaire fully or partially. Prior to sampling, oral fluid sampling was the most acceptable test (107/132, 81%) followed by throat swabs (80/134, 59%), nose swabs (77/132, 58%), and blood tests (48/130, 37%). Younger students were more nervous about all tests than older students but, after completing their tests, most children reported a “better than expected” experience with all the investigations. Students were more likely to agree to additional testing for nose swabs (93/113, 82%) and oral fluid (93/114, 82%), followed by throat swabs (85/113, 75%) and blood tests (72/108, 67%). Parents (n = 3,994) and staff (n = 2,580) selected a preference for weekly testing with nose swabs, throat swabs or oral fluid sampling, although staff were more flexible about testing frequency. Conclusions Primary school staff and parents were supportive of regular tests for SARS-CoV-2 and selected a preference for weekly testing. Children preferred nose swabs and oral fluids over throat swabs or blood sampling.