A clastic gas reservoir with unconsolidated sandstone layers present great challenges for an effective development, because the tendency of these layers to produce sand. The objective of this paper is to present and highlight the applications of geomechanics in predicting critical drawdown pressure during the completion design and flowback test design with the ultimate purpose of minimizing the sand production. This paper will evaluate the perforation strategy for wells that may be prone to produce sand as part of the completion design optimization. A geomechanical approach was implemented to evaluate the interaction between stress field and the mechanical properties of rocks. A 1-D Mechanical Earth Model (MEM) was built and calibrated with offset wells in the nearby area. The overburden pressure was calculated by integrating density logs from the offset wells. The minimum horizontal stress was calibrated using closure pressure derived from the offset fracture analysis carried out in the offset wells. The rock elastic properties were calibrated with lab test data from an offset well locate ~2 km away from Well_A. Two case studies will be presented in this paper. The first case is Well_A drilled in a Devonian clastic reservoir, this vertical gas well was perforated with 60 degrees phasing guns. The well had a good performance during the flow back but the production was short-lived due to significant sand production. The second case is a blind test to validate the robustness of the methodology used in the first case study. An integrated approach was used to determine the most optimum way to perforate similar wells that has a potential to produce sand. Modified Lade failure criterion was used to predict the critical drawdown pressure because it takes into account the intermediate stress along with other geomechanical properties.

Predicting gravel pack performance is a complex and difficult task. Current practices account for expectation of performance by assigning a range of skin values that consider all the mechanisms that generate formation damage in the gravel pack. Other methods of identifying damage in the gravel pack include pressure build up analysis and the use of logging tools to investigate gravel placement. Using techniques such as NODALÒ analysis, overall well performance can be validated and the level of damage within the gravel pack estimated. This practice assumes that other damaging mechanisms present at the sand face are part of the overall gravel pack damage. This paper presents a methodology that integrates near wellbore damage, such as solid's invasion and mechanical damage during drilling, with damage caused to the gravel pack by solid particles as the well is started up for the first time. The model developed is supported by a laboratory test program of granular filter media to determine the various pore blocking mechanisms present during well start up. The results of this work indicate that impairment of the granular filter media is a function of flow rate, particle concentration and particle sizes. The final inflow model developed takes into account the volume of solids (mud cake and sand particles) that will be dragged into the gravel pack causing impairment. The result is an inflow profile from the gravel pack to the wellbore on a foot-by-foot basis that will dictate the final reservoir contribution and flow rates at the internal side of the screen. Background Reservoir contribution to production or inflow is highly influenced by its original and impaired petrophysical properties such as porosity and permeability. A similar analogy can be made for sand face completions that utilize granular filter media such as gravel packs or frac & packs (1). The main difference is that, in granular filter media, property such as permeability is constant and do not depend on geological or depositional conditions. Determination of reservoir permeability is carried out using a laboratory test that is then calibrated with another petrophysical property such as porosity, which can be derived on a continuous basis. Permeability of granular filter media such as gravel or proppant is normally specified by the manufacturer after detailed testing. It is considered that its size might vary depending on the manufacturer's quality control process. Table 1 presents various properties for gravels and proppants commercially available. In order to characterize reservoir inflow, it is imperative to determine the level of impairment caused during drilling and completion. This involves determination of the magnitude of each skin component along the exposed and contributing formation. Currently this is somewhat simpler for open hole completions, as it is assumed that although the contribution is not equal on a foot by foot basis current practices assume that it is even throughout the interval. Impairment is sometimes determined by running return permeability tests on reservoir core samples. These tests quantify the change in permeability that results due to mud invasion and the remaining permeability after simulated start up production conditions. Figure 1 illustrates the results obtained from such a test for an Andrew sandstone reservoir in the UKCS.

A huge oil recovery opportunity waits in the reservoirs of mature oil fields. Reviving mature oil fields through advancements in oil recovery has opened the doors to renewed hydrocarbon production from wells that have been forgotten because of the natural depletion after years of providing. One of these advancements is the effect of surging existing perforations using atmospheric chambers to create a dynamic underbalance at the instant perforations are created has been used in other oil and gas assets worldwide to improve production and, consequently, return on investment (ROI). This production increase was achieved with surge chambers to clean existing perforations. This technology allows producers to obtain sustained higher productivity from their wells at a low cost. This system creates an instantaneous in-situ negative pressure in the wellbore that surges and cleans the perforated interval improving the wells inflow conditions. It is relatively inexpensive to treat a well because it can be deployed on wireline, slickline, jointed tubing, or coiled tubing (CT). These various deployment methods also make this technology available for rigless interventions. This process uses fast-opening surge vents and atmospheric chamber assemblies that are activated milliseconds after the creation of perforations in the casing and perforation tunnels in the hydrocarbon reservoir. The dynamic underbalance in the wellbore surges these perforation tunnels, enabling the removal of debris and crushed material created by the high energy output of the explosive shaped charges. This technique can be used to clean existing perforations that have become plugged-off or restricted as a result of scale buildup over time. To achieve this, the vent and chamber assembly are run without the perforating gun assembly. This technology has been successfully used on rigless wireline operations, and in tubing-conveyed operations. The results have shown that it is possible to regain initial production rates at a relatively low cost as compared to other near-wellbore (NWB) stimulation techniques. This perforate and surge technique has also been used to reduce the operator's cost and time associated with a hydraulic fracturing operation in sandstone reservoirs. In scale-removal applications, this surge technique has been used to successfully remove barium sulfate (BaSO4). To validate these operations, using high-speed pressure/temperature recorders is recommended to capture the dynamic event (Schatz 1999). In addition to the hardware associated with the vents, chambers, and perforating guns, a software component is used to accurately predict the amount of dynamic underbalance in a specific bottomhole assembly (BHA) to achieve the best perforation cleanup to maximize well productivity.