Geophysical Engineering

AVO Inversion and Spectral Decomposition analysis on 106 Km2 of 3D seismic data has been successfully used to define the distribution of thin sand layers deposited in a deltaic setting from Ripah Field, Jabung Block, South Sumatra Basin.

Conventional attribute and interpretation methods provide limited access in delineating a highly heterogeneous reservoir distribution. Thin sands interbeded, abundant coal layers, and complex structure orientation complicates interpretation in developing and managing the field. High frequency seismic restoration method is used to improve
seismic resolution and further AVO Inversion and Spectral Decomposition analysis can be used to delineate this complex geological feature.

This combined interpretation between AVO Inversion and Spectral Decomposition shows distribution and orientation of reservoir targets, which are consistent with wells data. Result of this study has significantly minimized the risk for proposing development wells.

Jabung Block, in the northern edge of the South Sumatra Basin, actively explored since 1993 and currently operated by PetroChina. More than 200 wells have been drilled, producing average of 60,000 BOEPD from multiple different reservoirs. The present block boundary remains 20% (1642 sqkm) of its original after the final relinquishment in 2003, adds challenges of exploration strategy having narrow and mature block. To overcome this issue, advance seismic approaches such as Seismic Multi Attribute, AVO, Inversion, and AVO-Inversion, should be applied instead of conventional interpretation. This technique can not be applied homogenously and should follow the characteristic of each field in different formation targets. The Rock Physics analysis has been investigated for feasibility reservoir as well as hydrocarbon characterization covers entire Jabung area.

Rock physics analysis conducted by using electrical log data of around 50 assigned wells distribute and represent all different provenance area in the block. The study focused on lithology differentiation and hydrocarbon response to seismic data by deriving physical properties parameter from log data such as Impedance, Lame constant (Lambda and Mu), Bulk Modulus, Poisson Ratio, and Elastic Impedance in constant angle. Logs were cross-plotted to define facies correspond to reservoir/ or non-reservoir and correspond to hydrocarbon versus non-hydrocarbon. Hydrocarbon response analysis using by Zoeppritz equation was also applied to see AVO response. The result then mapped to see the Jabung reservoir (sand) distribution defined by rock physics parameter and AVO classes.

The result shows that different field with different formation targets in Jabung Block may have different rock physics parameter. AVO responses are also unique in different provenance/ region. Study result will then assist exploration strategy of using this proper technique to define sand distribution and hydrocarbon response in seismic data out of existing fields. It has been applied to convince and rank potential prospects exist in the area.

Seismic multi attribute analysis of 3D seismic data presents a great opportunity for reservoir characterization. Correlation between combined various P-wave seismic attributes and existing wells has been applied to 60 km 2 of seismic over a A-Sand reservoir in Southwest Betara (SWB) Field of Jabung Block, South Sumatra Basin. The field has produced oil since first production in late 2005 from the A-Sand Formation. To generate A-Sand subsurface attribute distribution maps, interpretive systems were used to process the 3D PSTM and well data.

The main problem in SWB is strong reflectivity orientation caused by the geometry of its structure which affects seismic resolution in A-Sand reservoir. A seismic multi attribute study has been carried out to solve this problem. Results indicate that this study was reliable in determining the best location for a new well SWB-3ST. By generating Sweetness attribute Instantaneous Frequency and Instantaneous Amplitude using certain equations, it shows similarity of A-Sand distribution compared to Sum Negative Amplitude attribute. These attributes can be used to delineate the A-Sand geological feature in SWB.

Both Sweetness and Sum Negative Amplitude attributes provides the distribution and orientation of reservoir targets consistent with well data. It has been successfully used to define the distribution of A-Sand layers deposited in a fluvial system setting at SWB Field, Jabung Block. Result of this study has significantly minimized the risk of proposing additional development well locations.

Konsep turbidit diperkenalkan pada tahun 1950. Kuenen dan Migliorini (1950) mendefinisikan turbidit sebagai suatu sedimen yang diendapkan oleh mekanisme arus turbid (turbidity current), sedangkan arus turbid itu sendiri adalah suatu arus yang memiliki suspensi sedimen dan mengalir pada dasar tubuh cairan, karena mempunyai kerapatan atau densitas yang lebih besar daripada cairan tersebut.

Turbidit adalah endapan langsung dari arus turbid, maka dapat ditemukan pada setiap lingkungan pengendapan dimana arus turbid atau kerapatan arus (density current) bekerja. Linkungan penendapan tersebut adalah danau dan waduk (reservoir), delta bagian depan (delta fronts), continentai shelves, dan yang terpenting adalah pada cekungan laut dalam.

Kebutuhan untuk memperluas pencarian sumber energi di lingkungan laut dalam semakin diintensifkan kepada pentingnya pemahaman yang baik tentang continental slope baik secara keberadaannya maupun karateristiknya. Saat ini penggabungan konsep tektonik lempeng, seismik stratigrafi dan kemajuan teknologi seismik refleksi merupakan pendekatan yang baik untuk memahami perkembangan continental margins. Pemahaman ini lebih menekankan kepada histori gelologi itu sendiri dan potensi hidrokarbon pada continental slope.

Seperti kita ketahui bahwa endapan yang terjadi pada continental slopes akibat pengaruh gaya berat (gravity mass-flow) pada ujung shelf (shelf break) dan dapat membentuk reservoar hidrokarbon yang sangat luas. Reservoar tersebut merupakan endapan-endapan turbidit dan kipas bawah laut (submarine fans). Hal ini membuat lingkungan laut dalam menjadi lokasi eksplorasi hidrokarbon di masa yang akan datang.

The onshore portion of the Southwest Betara (SWB) Field is in the  Jabung Block of the South Sumatra Basin, approximately 250 km south of Singapore. This field, discovered in 2005, is currently operated by PetroChina International Jabung in partnership with Petronas Carigali and PT Pertamina (Persero).

This article describes a study whose main objective was seismic reservoir characterization on the A-Sand within the Lower Talang Akar Formation. The process qualitatively and quantitatively details the character of the reservoir using primarily seismic data with a primary focus on defining the net pay and porosity within the A-Sand.

Keberhasilan eksplorasi pada laut dalam (deepwater) di wilayah Indonesia dicapai pada penemuan lapangan Migas Merah Besar dan West Seno oleh Unocal Indonesia yang saat ini bernama Chevron Pacific Indonesia. Dari penemuan lapangan tersebut, berkembang menjadi 7 lapangan Migas yang berada pada laut dalam daerah cekungan (basin) Kutei. Lebih dari 6 trillion cubic feet (tcf) gas dan 200 million bbls minyak dan kondensat ditemukan pada lapisan batupasir zaman miosen atas pada lingkungan laut dalam ini (Saller, et. all. 2006).

Threshold-inversion method has been applied on 30 Km2 of West Betara (WB) field generated from 3D post-stack seismic data with the WB-1, WB-3 and WB-4 wells as control. Different reservoir properties and facies in WB structure become a challenge for the team to find relevant geophysical study on this field.

Threshold-inversion method is the combination interpretation method between threshold attribute and amplitude of seismic inversion cube to
distinguish and define the reservoir distribution within certain cut-off  value.

The map is showing the delineation of conglomeratic and coarse  grained sandstone reservoirs with NE-SW direction, which is consistent with well data. The result has been successfully used to distinguish and to define the distribution of oil reservoir in Lower Talang Akar Formation (LTAF) and minimize the risk for infill wells location.

Seismic reservoir characterization of a 3D seismic and well data has been applied to 60 km2 of seismic over Lower Talang Akar Formation sand reservoirs intervals in Southwest Betara Field of Jabung Block, South Sumatra Basin, Indonesia. The field has produced oil since first production in late 2005 from the sandstone-A reservoirs. The main problem on this field is well distributed of coals on sandstone-A reservoirs interval which affecting seismic reflectivity and shows the ambiguity between coals and sandstone-A reservoir. The objectives of this study are to delineate sandstone-A reservoir distribution laterally by using seismic reservoir characterization methods and to compare the result with previous study.

The sensitivity analysis from log data, seismic multi-attribute and amplitude attribute study has been carried out to solve this problem. Results from crossplot analyses of well data indicate that the coals can be identified and distinguished over and between the sandstone reservoirs by using pseudo log Gamma Ray Index (GRI) within certain cutoff value. By using this pseudo log GRI and generating multi-attribute analysis with linear regression, the GRI volume has been created. Based on this GRI volume, the lateral distribution of sandstone-A reservoir and coals can be created separately by using amplitude attributes of RMS Amplitude, Threshold Value and Sum of Negative Amplitude. These attributes can be used to delineate the paleo depositional environment of sandstone-A reservoir and coals in Southwest Betara Field.

The distribution maps are showing the delineation of sandstone-A reservoirs and coals with NW-SE direction, which is consistent with well data. By comparing these data to the previous study, the result of latest study has been successfully differentiates the sand reservoir and coals, also defines both in laterally distribution within Southwest Betara Field.

Azuni Field is located on South Sumatra Basin was discovered in 2004 and since 2006 this field producing oil from Lower Talang Akar Formation (LTAF). This field also has potential gas reservoir in Gumai Formation (GUF). There are two main potential gas reservoirs in this formation, Sand-11 and Sand-12 which are potentially to be developed in the next phase. The Gumai sand formation is relatively thick that represents pro-deltaic environments depositional system. The seismic section over this interval indicate alternating peak and through which may indicate the presence of sand reservoir layers alternating with shale. To generate Gumai reservoir distribution map of Sand-11 and Sand-12, probabilistic neural network (PNN) analysis based on multi-attribute utilizing 3D PSTM seismic data and 14 wells has been applied.

Based on sensitivity analysis, sands and shales which representing reservoir and non-reservoir can be differentiated from density log. A statistical approach, including multi-attribute and PNN analysis were used to derive the relationship between attributes of the seismic data and density log. The established relationship was used to estimate pseudo density at each seismic trace on the 3-D.

The results of PNN analysis indicated that four attributes show high correlation 0.86 of log density properties in the study area. This method provides the distribution and orientation of reservoir targets consistent with well data. It has been successfully used to define the distribution of Sand-11 and Sand-12 of GUF. In future this study result will advance the petroleum development activities in the area.

West Betara (WB) Field is located in South Sumatra Basin, Indonesia, tested hydrocarbon (Gas) from carbonate reservoirs of the Batu Raja Formation. This is an interesting challenge to describe the lateral distribution and its property within carbonate reservoir at minimum data information. The objectives of this study are to delineate carbonate reservoir distribution including the laterally rock properties by using seismic reservoir characterization methods.

The availability of 3D seismic data, DST's data, conventional well data as wireline and mudlog data is very helpful in answering the challenge. By optimizing well data information, the sensitivity analysis can be generated from wireline log data to determine gas zone and appropriate seismic reservoir characterization method. 3D Seismic data provides a helpful inter-well information for determining and visualizing reservoir structure and rock properties at the present day, they also help us to generate seismic inversion model and multi-attribute analyses to predict reservoir boundary and its property distribution laterally.

The sensitivity analysis of cross-plots combination from Gamma Ray Log, Acoustic Impedance (AI) Log derived from Sonic and density log, Neutron-Porosity Log and Resistivity Log shows good separation for gas zone in carbonate reservoir. The results help us to predict reservoir boundary and its property distribution laterally by seismic inversion and multi-attribute method in our 3D seismic data. The Gamma-ray (low value) and AI (high value) maps are showing consistency of carbonate reservoir delineation. In line with Gamma-ray and AI maps, the porosity map of the carbonate reservoir shows gas zone (high value) with certain pattern and it is consistent with tested well data.

Exploration of fractured basement reservoirs has become a great subject of interest in oil and gas industries due to depleting hydrocarbon reserves in many conventional sources. In 2013, PetroChina Intl. Jabung Ltd. successfully drilled the Northeast Betara (NEB) Base-1 well located in South Sumatra Basin to 3000' MD / 2000' TVD through the basement, primarily targeting a fractured basement reservoir. Barefoot test showed that gas and condensate flowed from the fractured basement. Following the success of NEB Base-1 well drilling, NEB Base-2 well was drilled in 2015 at a greater depth than NEB Base-1 well to reach the basement. Interestingly, the barefoot test in NEB Base-2 well showed no indication of influx from the well. Therefore, further investigation on the fracture characteristics from both wells was conducted to better understand their effects on hydrocarbon accumulation.

Mudlog and gamma ray log data suggested that both wells have similar granitic basement lithology. However, image log data showed resistivity contrast enhancement for NEB Base-1 well which was associated with open fractures. On the other hand, limited resistivity contrast was observed in NEB Base-2 well, suggesting that the fractures were closed or filled with minerals. The fracture orientation of NEB Base-1 well also indicated that the fracture azimuth is oriented towards ENE-WSW, which is in the direction of compressional tectonics. In contrast, the fractures observed in the NEB Base-2 well are oriented towards NNE-SSW orientation, which is in the direction of extensional tectonics. In addition, compressional sonic data from NEB Base-1 well showed more cycle skipping compared to NEB Base-2 well and NEB Base-1 resistivity log is lower than in NEB Base-2 well.

The differences in fracture characteristics of both wells were attributed to the difference in their stratigraphic succession during the syn-rift phase of basin evolution. Palinspastic reconstruction in the NEB area suggested that the area of NEB Base-1 experienced inversion or uplift in the post-rift phase. However, there is no indication of inversion after the syn-rift phase around the NEB Base-2 area. Hence, tectonic inversion played an important role in determining the location of hydrocarbon accumulations in the fractured basement.

Betara structure is located in the northern part of South Sumatra Basin (SSB). It is formed by the mega sequence tectonic processes of rifting and inversion with various stratigraphic sequences from land to marine. Referring to the schematic map of global overpressure occurrences, most of Indonesia including Sumatra is an overpressure region. The indications of overpressure zones in the Betara structure are in Gumai and Talang Akar Formations where the syn-rift to post-rift sequence is dominated by fine grained sediments (shale) with low permeability. A preliminary study has been conducted with available data to predict the type of overpressure mechanism in the Betara structure.

Existing data such as XRD, pressure (RFT/MDT), drilling parameters, wireline log suites and geochemistry are used to determine the overpressure zones. The presence of overpressure zones is marked by a significant reversal of sonic log with increasing depth from the normal compaction trend on several existing wells. Crossplot analysis of Th/K (clay typing), Sonic vs. Density, and vitrinite reflectance are used to analyze the causative overpressure mechanism that occurs in the Betara structure.

Results showed overpressure indications in the Betara structure with low overpressure characteristic in the Gumai interval and with increasing depth overpressure decreased to almost equal hydrostatic pressure in the lower part of near Baturaja Formation. High overpressure occurs in the Upper Talang Akar interval and it decreased or back to hydrostatic pressure in the Lower Talang Akar interval. Based on preliminary study analysis, it can be predicted that the overpressure mechanism in the Gumai interval is possibly caused by disequilibrium compaction of thick shale layer whereas in Talang Akar it is caused by clay minerals transformation and hydrocarbon maturity as a result of the temperature influence.

Wavelet is an important parameter for tying well to seismic data. Frequency and phase from wavelet highly affect the correlation coefficient result from tying process. There are several methods has been used in this study to generate an optimum single wavelet with good correlation coefficient for seismic data interpretation and also as a preliminary analysis to show the influence of external pressure to formation pressure indirectly.

24 wells of RPH Field were applied in this study and the target is thin reservoirs from Lower Talang Akar Formation. The methods which used to estimate an optimum single wavelet are statistical method, deterministic method and hybrid method. The generated wavelets from different methods are used to create synthetic seismogram and correlated it with real seismic trace in order to produce good correlation coefficient. By analyzing the change of velocity and the phase of wavelet in each well indirectly revealed the relationship of the phase and the formation velocity corresponding to formation pressure due to external pressure.

Based on comparison of analysis result from all methods, an optimum wavelet which used for interpretation is wavelet from hybrid method. Its average phase is 30˚ at the dominant frequency of 45 Hz. It yields average correlation coefficient of 0.775. The result of phase, velocity, and pressure analysis show that the phase change is influenced by the difference of velocity due to external pressure. The seismic phase tends to positive when the formation velocity and formation pressure is increase. The distribution of velocity and phase in this field indicates that the Lower Talang Akar formation in lower structure is more affected by pressure than those in higher structure. So, the lower structure has higher velocity and more positive in seismic phase.

AVA (Amplitude Versus Angle) is one of geophysical method for detecting hydrocarbon existence by observing the amplitude characteristic while increasing incidence angle of wave which caused by the existence of a fluid anomaly especially gas in reservoir. Conglomerate reservoir in NEB Field has proven to be a gas reservoir. It is a challenge to describe the presence of gas in this reservoir laterally. Preliminary study has been conducted by implementing the synthetic seismic modeling to investigate the AVA response of reflectors from the conglomerate reservoir in the NEB Field.

From well data parameter and Aki-Richard equations (1980), the synthetic Seismic models are generated and transforms into angle of incidence function. FRM (Fluid Replacement Modeling) is used to analyze the differences of synthetic seismic model at in-situ and wet conditions.

Result shows conglomerate reservoir in NEB Fields classified into class 4 based with the character of the amplitude of the intercept is negative and forms flat gradient with slightly increased. Based on Poisson's Ratio with Vp/Vs Ratio cross-plot analysis, the reservoir conglomerate has a value of Poisson's ratio approximately 0.24 in the gas case with a value of Vp/Vs is 1.7, while in the wet case has a value of Poisson's ratio of about 0.34 to the value of Vp/Vs is 1.8. The surface reservoir distribution is extracted from seismic 3D angle stack data volume which have near zero value at conglomerate reservoir with gas potential.

Jabung block is one of the most productive blocks in Indonesia with its main reservoir in Talang Akar Formation. As a step to optimize the production in the existing fields, PetroChina International Companies (Indonesia) as the operator, continues to explore the eastern part of this block and has successfully drilled exploration wells in Manuk Field. The primary target is the Lower part of Talang Akar Formation (LTAF) which is characterized by thin sandstones and thus become the main problem to determine reservoir distribution.

To minimize the uncertainty of the reservoir distribution prediction, some seismic reservoir characterization methods such as simple AVA (Amplitude Variation with Angle of incidence) and hybrid seismic attribute methods are implemented by using existing wells and Post-Stack 2D seismic data. Both methods are useful tools to determine thin reservoir distribution in Manuk Field.

Mungkin Anda pernah bertanya-tanya bagaimana suatu konser musik besar yang diadakan di stadion dengan banyak penonton bisa sukses. Atau mungkin Anda pernah berjalan melewati suatu konstruksi gedung bertingkat dan kemudian berpikir, “Bagaimana proyek konstruksi bangunan sebesar ini yang membutuhkan dana besar dan melibatkan orang banyak bisa berjalan begitu lancar?”. Jawabannya adalah manajemen proyek.

Tidak ditemukan sumber yang pasti mengenai bagaimana sejarah manajemen proyek yang sebenarnya. Namun, manajemen proyek telah diterapkan dari awal perabadan manusia.  Sebelum munculnya manajemen proyek atau sejarahnya, prinsip manajemen dan organisasi dijalankan atas dasar hubungan, koneksi dan kepercayaan yang dibangun selama bertahun-tahun.

Pada setiap proyek terdapat risiko. Terlebih lagi pada proyek-proyek besar, banyaknya keputusan yang harus diambil membuat banyaknya kemungkinan hambatan dan risiko yang akan muncul. Untuk menghindari risiko-risiko tersebut, kita bisa mencari jalan keluar dengan mempertimbangkan segala kemungkinan yang dapat terjadi.

Agar suatu proyek bisa berjalan lancar menuju tujuan proyek dengan spesifikasi yang telah ditentukan di awal, diperlukan manajemen proyek yang baik. Pada proses ini, banyak hal seperti anggaran, tenggat waktu, dan lingkup proyek harus direncanakan. Ini berarti bahwa pekerjaan-pekerjaan tertentu akan lebih efisien dan efektif jika dikelola dalam kerangka proyek dan bukan diperlakukan sebagai pekerjaan biasa. Dengan demikian diperlukan penerapan manajemen proyek secara baik dan benar.