TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAcid fracturing has been part of Saudi Aramco's gas development strategy to maximize productivity from for vertical wells in the Khuff carbonates over the last several years. During acid fracturing, the wormholes created by the reaction with the formation results in excessive fluid loss. Controlling fluid loss is one of the key objectives in acid fracturing treatments to be able to create longer and wider fractures, and hence maximize well productivity. Alternating stages of polymer pad with diesel emulsified acid for deeper penetration and in-situ gelled acid, a polymer-based system, have been extensively used in most fracture treatements in an attempt to control excessive leak-off during the treatment.

A clastic gas reservoir, have been characterized of being unconsolidated in nature, as well as its complexity and heterogeneity. Regarding to the ability to transmit fluids, this reservoir is predominantly tight with a wide variation in the permeability range, which confirms its heterogeneity. The depositional environment interpretation suggests the presence of channels running from West to East direction with kind of limited lateral extension. In terms of well completion strategy, most of the wells have been proppant fractured to produce at sustainable rates. Pressure transient analysis (PTA) has been applied extensively to better characterize and understand the reservoir behavior, well performance and to obtain significant properties of the reservoir. The challenges of this work consisted of performing a critical review of the existing PTA to identify some common behaviors or general trends in the pressure response. Considering the PTA have assessed the same reservoir and that several wells have been completed with similar completion techniques was expected finding similar pressure response behaviors. This paper presents different cases that have been analyzed through PTA, summarizing common trends, in terms of reservoir behavior and well response that have been observed during the study. The outputs of this study were used as inputs for the simulation reservoir models to narrow the uncertainty in some reservoir and wellbore properties and as inputs for the static model construction to better understand or confirm geological assumptions. The results of the PTA interpretation also helped to successfully drill newer wells away from any geological complexity and achieved the planned target of gas rates.

Acid fracturing as stimulation treatment for lower permeability multilayered reservoirs has been extensively used for carbonate formations around the world. For multilayered reservoirs, the success of stimulation is highly dependent on the fracture capability to connect the layers, fluid leak-off, fracture geometry and stimulation fluid properties. In Khuff carbonate reservoir from Ghawar Field, the heterogeneous nature of the multilayered formation, temperature, layers separation and especially wellbore deviation along the interval to be stimulated present additional technical challenges for fracturing stimulation and all of them has been addressed by incorporating Associative Polymer blends as a separate step to assure an effective fracturing stimulation fluid diversion.The paper will show a case study for gas well in Ghawar field where an effective diversion technique with Associative Polymers was used successfully in fracturing treatments which resulted in enhancing more of tight layers contribution and increased total productivity by more than an order of magnitude. Associative Polymer (AP) blended in an innovative way forming, a solids or fibers free non-reactive water base system. The new diversion system was successfully used in several gas wells completed in Khuff carbonate reservoir where clear diversion and acid reaction signatures have been implied by surface and bottom-hole pressure (BHP) data recorded during the entire treatments. Production increases in addition to Pressure Buildup (PBU) and Production Logging corroborated the flow contribution from all the perforated intervals included tight layers, which contrasts with offset producers previously treated with other types of diverting agents.The paper will present for the first time the treatment design and benefits of AP blend diverting agent usage for acid fracturing stimulations. A case history where the wellbore orientation is 45 degree is going to be presented and discussed in detail. Field case shows that the wellbore deviation was not a limitation for the effective stimulation and for the AP blend system to work. In addition, this paper will provide some guidelines for potential use of this diverting agent and candidate selection, treatment design, and execution.

Dealing with tight high pressure/high temperature (HPHT) sour gas reservoirs encounters many challenges. One challenge associated with these reservoirs is the development of hard and heavy scale mixture in the production tubing, causing flow and accessibility restrictions. To restore full accessibility, a mechanical de-scaling operations using special milling and cleanout assemblies is the best current solution to this problem, due to the fact that chemical dissolving methods do not deliver the desired results. Another challenge is conventional perforation in some tight wells gives limited penetration, which does not establish the required wellbore reservoir communication. In this case, utilizing the abrasive jetting tool will offer the best solution to overcome the casing string, cement, formation damage achieve optimum penetration which will optimize the stimulation design and enhance the well productivity. In recent years, using coiled tubing (CT) equipped with fiber optics with aforementioned coil tubing intervention operations, have become a common practice in gas wells. Using this system provides the ability to acquire on-job real time data such as pressure, temperature and gamma ray depth correlation. Furthermore, the incorporation of a new rugged fiber optics system into the intervention strategy has enabled increasing operational success rate and results in robust control on the operation parameters, minimizing the risk of gas influx, reducing coil tubing runs and improving decision making process during the operations. This paper describes the challenges in mechanical de-scaling and slot cuttings operations, overview of different applications using CT with fiber optics system, provides a comparison between the rugged and standard fiber optics systems and lessons learned of recent implementation of the rugged CT fiber optic system.

Drilling in thin reservoirs is challenging task. But with easy pockets gone the reservoirs left are less than 5 to 10 feet and it becomes difficult to steer well exclusively in the sweet spot or sand in thin payzone. It is this reservoir which offer task to drill horizontal well and produce maximum where otherwise it would be difficult to produce even 200-300bopd from this thin layer of silty shales. Moreover the thin beds are like appearing or vanishing as we drill ahead due to facies change. This needs complete attention till the well reaches Target Depth (TD). Even a small fault of sub-seismic nature of 2 feet throw can offset the well from the sweet zone. But with advanced logging tools used in two wells helps to understand the nature of lithology and its productivity. Best application of this tools are in silty shales in Burgan Sands Upper (BGSU) which generally show high GR and often this leads to misjudgment of well not being in sweet spot. Logging While Drilling (LWD) logs and inversion was used whether the well is in productive zone or not. The LWD tools now have Azimuthal GR, density and resistivity. This gives a holistic picture of the lithology in the roof side or the bottom side of the lateral section. The wells under discussion were drilled with such advanced version of distance to boundary tool. After well was steered till TD, the data was processed by Petro-physicist to indicate possible payzone to decide completion. But due to high GR which is often prevalent in Burgan Sand Upper (BGSU) the entire well bore was not getting classified as potential payzone. But after looking the inversion and all LWD data sets it was conveyed that the Inflow Control Device (ICD) can be lowered for entire well bore length. As an outcome advanced ICD was lowered also against high GR zones which otherwise were not getting classified as potential payzone, and well were completed. The well was put on production starting with 1300 BOPD on 32″ choke and still after 18 months continues to produce. PLT results show that the zones indicating high GR and with poor log properties were also contributing oil. The paper discusses these wells and utilization of complete data set acquired at time of drilling and taking completion decision accordingly. The output of data of LWD has been fully utilized to complete the well successfully and given the confidence of doing so in other wells. In fact this experience was used in another similar looking well with unfavorable parameters and successfully completed.